[PATCH hmm v2 0/5] Adjust hmm_range_fault() API

[PATCH hmm v2 0/5] Adjust hmm_range_fault() API

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

The API is a bit complicated for the uses we actually have, and
disucssions for simplifying have come up a number of times.

This small series removes the customizable pfn format and simplifies the
return code of hmm_range_fault()

All the drivers are adjusted to process in the simplified format.
I would appreciated tested-by's for the two drivers, thanks!

v2:
 - Move call chain to commit message
 - Fix typo of HMM_PFN_REQ_FAULT
 - Move nouveau_hmm_convert_pfn() to nouveau_svm.c
 - Add acks and tested-bys
v1: https://lore.kernel.org/r/0-v1-4eb72686de3c+5062-hmm_no_flags_jgg@mellanox.com

Cc: Christoph Hellwig <hch@lst.de>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
To: Ralph Campbell <rcampbell@nvidia.com>
Cc: nouveau@lists.freedesktop.org
Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: "Kuehling, Felix" <Felix.Kuehling@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: "Yang, Philip" <Philip.Yang@amd.com>
To: linux-mm@kvack.org

Jason Gunthorpe (5):
  mm/hmm: make CONFIG_DEVICE_PRIVATE into a select
  mm/hmm: make hmm_range_fault return 0 or -1
  drm/amdgpu: remove dead code after hmm_range_fault()
  mm/hmm: remove HMM_PFN_SPECIAL
  mm/hmm: remove the customizable pfn format from hmm_range_fault

 Documentation/vm/hmm.rst                |  28 ++--
 arch/powerpc/Kconfig                    |   2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  56 +++----
 drivers/gpu/drm/nouveau/Kconfig         |   2 +-
 drivers/gpu/drm/nouveau/nouveau_dmem.c  |  27 +---
 drivers/gpu/drm/nouveau/nouveau_dmem.h  |   3 +-
 drivers/gpu/drm/nouveau/nouveau_svm.c   |  94 ++++++++----
 include/linux/hmm.h                     | 109 +++++---------
 mm/Kconfig                              |   7 +-
 mm/hmm.c                                | 185 +++++++++++-------------
 10 files changed, 217 insertions(+), 296 deletions(-)

-- 
2.26.2

[PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a select

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

There is no reason for a user to select this or not directly - it should
be selected by drivers that are going to use the feature, similar to how
CONFIG_HMM_MIRROR works.

Currently all drivers provide a feature kconfig that will disable use of
DEVICE_PRIVATE in that driver, allowing users to avoid enabling this if
they don't want the overhead.

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 arch/powerpc/Kconfig            | 2 +-
 drivers/gpu/drm/nouveau/Kconfig | 2 +-
 mm/Kconfig                      | 7 +------
 3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 924c541a926008..8de52aefdc74cc 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -455,7 +455,7 @@ config PPC_TRANSACTIONAL_MEM
 config PPC_UV
 	bool "Ultravisor support"
 	depends on KVM_BOOK3S_HV_POSSIBLE
-	depends on DEVICE_PRIVATE
+	select DEVICE_PRIVATE
 	default n
 	help
 	  This option paravirtualizes the kernel to run in POWER platforms that
diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
index d6e4ae1ef7053a..af5793f3e7c2cf 100644
--- a/drivers/gpu/drm/nouveau/Kconfig
+++ b/drivers/gpu/drm/nouveau/Kconfig
@@ -86,10 +86,10 @@ config DRM_NOUVEAU_BACKLIGHT
 
 config DRM_NOUVEAU_SVM
 	bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
-	depends on DEVICE_PRIVATE
 	depends on DRM_NOUVEAU
 	depends on MMU
 	depends on STAGING
+	select DEVICE_PRIVATE
 	select HMM_MIRROR
 	select MMU_NOTIFIER
 	default n
diff --git a/mm/Kconfig b/mm/Kconfig
index c1acc34c1c358c..7ca36bf5f5058e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -805,15 +805,10 @@ config HMM_MIRROR
 	depends on MMU
 
 config DEVICE_PRIVATE
-	bool "Unaddressable device memory (GPU memory, ...)"
+	bool
 	depends on ZONE_DEVICE
 	select DEV_PAGEMAP_OPS
 
-	help
-	  Allows creation of struct pages to represent unaddressable device
-	  memory; i.e., memory that is only accessible from the device (or
-	  group of devices). You likely also want to select HMM_MIRROR.
-
 config FRAME_VECTOR
 	bool
 
-- 
2.26.2

Re: [PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a select

[John Hubbard]

On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> There is no reason for a user to select this or not directly - it should
> be selected by drivers that are going to use the feature, similar to how
> CONFIG_HMM_MIRROR works.

Yes, this is a nice touch.

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA

> 
> Currently all drivers provide a feature kconfig that will disable use of
> DEVICE_PRIVATE in that driver, allowing users to avoid enabling this if
> they don't want the overhead.
> 
> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> ---
>   arch/powerpc/Kconfig            | 2 +-
>   drivers/gpu/drm/nouveau/Kconfig | 2 +-
>   mm/Kconfig                      | 7 +------
>   3 files changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 924c541a926008..8de52aefdc74cc 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -455,7 +455,7 @@ config PPC_TRANSACTIONAL_MEM
>   config PPC_UV
>   	bool "Ultravisor support"
>   	depends on KVM_BOOK3S_HV_POSSIBLE
> -	depends on DEVICE_PRIVATE
> +	select DEVICE_PRIVATE
>   	default n
>   	help
>   	  This option paravirtualizes the kernel to run in POWER platforms that
> diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
> index d6e4ae1ef7053a..af5793f3e7c2cf 100644
> --- a/drivers/gpu/drm/nouveau/Kconfig
> +++ b/drivers/gpu/drm/nouveau/Kconfig
> @@ -86,10 +86,10 @@ config DRM_NOUVEAU_BACKLIGHT
>   
>   config DRM_NOUVEAU_SVM
>   	bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
> -	depends on DEVICE_PRIVATE
>   	depends on DRM_NOUVEAU
>   	depends on MMU
>   	depends on STAGING
> +	select DEVICE_PRIVATE
>   	select HMM_MIRROR
>   	select MMU_NOTIFIER
>   	default n
> diff --git a/mm/Kconfig b/mm/Kconfig
> index c1acc34c1c358c..7ca36bf5f5058e 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -805,15 +805,10 @@ config HMM_MIRROR
>   	depends on MMU
>   
>   config DEVICE_PRIVATE
> -	bool "Unaddressable device memory (GPU memory, ...)"
> +	bool
>   	depends on ZONE_DEVICE
>   	select DEV_PAGEMAP_OPS
>   
> -	help
> -	  Allows creation of struct pages to represent unaddressable device
> -	  memory; i.e., memory that is only accessible from the device (or
> -	  group of devices). You likely also want to select HMM_MIRROR.
> -
>   config FRAME_VECTOR
>   	bool
>   
> 

Re: [PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a select

[Andrew Morton]

On Fri,  1 May 2020 15:20:44 -0300 Jason Gunthorpe <jgg@ziepe.ca> wrote:

> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> There is no reason for a user to select this or not directly - it should
> be selected by drivers that are going to use the feature, similar to how
> CONFIG_HMM_MIRROR works.
> 
> Currently all drivers provide a feature kconfig that will disable use of
> DEVICE_PRIVATE in that driver, allowing users to avoid enabling this if
> they don't want the overhead.
> 

I'm not too sure what's going on here, but i386 allmodconfig broke.

kernel/resource.c: In function '__request_free_mem_region':
kernel/resource.c:1653:28: error: 'PA_SECTION_SHIFT' undeclared (first use in this function); did you mean 'SECTIONS_PGSHIFT'?
  size = ALIGN(size, 1UL << PA_SECTION_SHIFT);

because in current mainline, allmodconfig produces
CONFIG_DEVICE_PRIVATE=n but in current linux-next, allmodconfig
produces CONFIG_DEVICE_PRIVATE=y.  But CONFIG_SPARSEMEM=n so the build
breaks.

Bisection fingers this commit, but reverting it doesn't seem to fix
things.  Could you take a look please?

I'm seeing this from menuconfig:

WARNING: unmet direct dependencies detected for DEVICE_PRIVATE
  Depends on [n]: ZONE_DEVICE [=n]
  Selected by [m]:
  - DRM_NOUVEAU_SVM [=y] && HAS_IOMEM [=y] && DRM_NOUVEAU [=m] && MMU [=y] && STAGING [=y]
  - TEST_HMM [=m] && RUNTIME_TESTING_MENU [=y] && TRANSPARENT_HUGEPAGE [=y]

`select' rather sucks this way - easy to break dependencies.  Quite a
number of years ago the Kconfig gurus were saying "avoid", but I don't
recall the details.

Re: [PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a select

[Jason Gunthorpe]

On Sat, May 09, 2020 at 05:16:12PM -0700, Andrew Morton wrote:
> On Fri,  1 May 2020 15:20:44 -0300 Jason Gunthorpe <jgg@ziepe.ca> wrote:
> 
> > From: Jason Gunthorpe <jgg@mellanox.com>
> > 
> > There is no reason for a user to select this or not directly - it should
> > be selected by drivers that are going to use the feature, similar to how
> > CONFIG_HMM_MIRROR works.
> > 
> > Currently all drivers provide a feature kconfig that will disable use of
> > DEVICE_PRIVATE in that driver, allowing users to avoid enabling this if
> > they don't want the overhead.
> > 
> 
> I'm not too sure what's going on here, but i386 allmodconfig broke.
> 
> kernel/resource.c: In function '__request_free_mem_region':
> kernel/resource.c:1653:28: error: 'PA_SECTION_SHIFT' undeclared (first use in this function); did you mean 'SECTIONS_PGSHIFT'?
>   size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
> 
> because in current mainline, allmodconfig produces
> CONFIG_DEVICE_PRIVATE=n but in current linux-next, allmodconfig
> produces CONFIG_DEVICE_PRIVATE=y.  But CONFIG_SPARSEMEM=n so the build
> breaks.

I think Arnd identified this, let us just revet the patch that caused
it.

> Bisection fingers this commit, but reverting it doesn't seem to fix
> things.  Could you take a look please?

There is a latter patch adding a 'select DEVICE_PRIVATE' so reverting
this needs to swap that to 'depends on'.

I've done both and updated git

Regards,
Jason

[PATCH hmm v2 2/5] mm/hmm: make hmm_range_fault return 0 or -1

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

hmm_vma_walk->last is supposed to be updated after every write to the
pfns, so that it can be returned by hmm_range_fault(). However, this is
not done consistently. Fortunately nothing checks the return code of
hmm_range_fault() for anything other than error.

More importantly last must be set before returning -EBUSY as it is used to
prevent reading an output pfn as an input flags when the loop restarts.

For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only
set last when returning -EBUSY.

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 Documentation/vm/hmm.rst                |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  4 ++--
 drivers/gpu/drm/nouveau/nouveau_svm.c   |  6 +++---
 include/linux/hmm.h                     |  2 +-
 mm/hmm.c                                | 25 +++++++++----------------
 5 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 4e3e9362afeb10..9924f2caa0184c 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -161,7 +161,7 @@ device must complete the update before the driver callback returns.
 When the device driver wants to populate a range of virtual addresses, it can
 use::
 
-  long hmm_range_fault(struct hmm_range *range);
+  int hmm_range_fault(struct hmm_range *range);
 
 It will trigger a page fault on missing or read-only entries if write access is
 requested (see below). Page faults use the generic mm page fault code path just
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 6309ff72bd7876..7eb745b8acce0f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -852,12 +852,12 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
 	down_read(&mm->mmap_sem);
 	r = hmm_range_fault(range);
 	up_read(&mm->mmap_sem);
-	if (unlikely(r <= 0)) {
+	if (unlikely(r)) {
 		/*
 		 * FIXME: This timeout should encompass the retry from
 		 * mmu_interval_read_retry() as well.
 		 */
-		if ((r == 0 || r == -EBUSY) && !time_after(jiffies, timeout))
+		if (r == -EBUSY && !time_after(jiffies, timeout))
 			goto retry;
 		goto out_free_pfns;
 	}
diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 645fedd77e21b4..c68e9317cf0740 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -536,7 +536,7 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 		.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT,
 	};
 	struct mm_struct *mm = notifier->notifier.mm;
-	long ret;
+	int ret;
 
 	while (true) {
 		if (time_after(jiffies, timeout))
@@ -548,8 +548,8 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 		down_read(&mm->mmap_sem);
 		ret = hmm_range_fault(&range);
 		up_read(&mm->mmap_sem);
-		if (ret <= 0) {
-			if (ret == 0 || ret == -EBUSY)
+		if (ret) {
+			if (ret == -EBUSY)
 				continue;
 			return ret;
 		}
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 7475051100c782..0df27dd03d53d7 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -120,7 +120,7 @@ static inline struct page *hmm_device_entry_to_page(const struct hmm_range *rang
 /*
  * Please see Documentation/vm/hmm.rst for how to use the range API.
  */
-long hmm_range_fault(struct hmm_range *range);
+int hmm_range_fault(struct hmm_range *range);
 
 /*
  * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
diff --git a/mm/hmm.c b/mm/hmm.c
index 280585833adfc1..f06bcac948a79b 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -174,7 +174,6 @@ static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
 	}
 	if (required_fault)
 		return hmm_vma_fault(addr, end, required_fault, walk);
-	hmm_vma_walk->last = addr;
 	return hmm_pfns_fill(addr, end, range, HMM_PFN_NONE);
 }
 
@@ -207,7 +206,6 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
 	pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
 		pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags;
-	hmm_vma_walk->last = end;
 	return 0;
 }
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -386,13 +384,10 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 		r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, pfns);
 		if (r) {
 			/* hmm_vma_handle_pte() did pte_unmap() */
-			hmm_vma_walk->last = addr;
 			return r;
 		}
 	}
 	pte_unmap(ptep - 1);
-
-	hmm_vma_walk->last = addr;
 	return 0;
 }
 
@@ -455,7 +450,6 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		for (i = 0; i < npages; ++i, ++pfn)
 			pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
 				  cpu_flags;
-		hmm_vma_walk->last = end;
 		goto out_unlock;
 	}
 
@@ -500,7 +494,6 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 	for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
 		range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
 				 cpu_flags;
-	hmm_vma_walk->last = end;
 	spin_unlock(ptl);
 	return 0;
 }
@@ -537,7 +530,6 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end,
 		return -EFAULT;
 
 	hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
-	hmm_vma_walk->last = end;
 
 	/* Skip this vma and continue processing the next vma. */
 	return 1;
@@ -555,9 +547,7 @@ static const struct mm_walk_ops hmm_walk_ops = {
  * hmm_range_fault - try to fault some address in a virtual address range
  * @range:	argument structure
  *
- * Return: the number of valid pages in range->pfns[] (from range start
- * address), which may be zero.  On error one of the following status codes
- * can be returned:
+ * Returns 0 on success or one of the following error codes:
  *
  * -EINVAL:	Invalid arguments or mm or virtual address is in an invalid vma
  *		(e.g., device file vma).
@@ -572,7 +562,7 @@ static const struct mm_walk_ops hmm_walk_ops = {
  * This is similar to get_user_pages(), except that it can read the page tables
  * without mutating them (ie causing faults).
  */
-long hmm_range_fault(struct hmm_range *range)
+int hmm_range_fault(struct hmm_range *range)
 {
 	struct hmm_vma_walk hmm_vma_walk = {
 		.range = range,
@@ -590,10 +580,13 @@ long hmm_range_fault(struct hmm_range *range)
 			return -EBUSY;
 		ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
 				      &hmm_walk_ops, &hmm_vma_walk);
+		/*
+		 * When -EBUSY is returned the loop restarts with
+		 * hmm_vma_walk.last set to an address that has not been stored
+		 * in pfns. All entries < last in the pfn array are set to their
+		 * output, and all >= are still at their input values.
+		 */
 	} while (ret == -EBUSY);
-
-	if (ret)
-		return ret;
-	return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+	return ret;
 }
 EXPORT_SYMBOL(hmm_range_fault);
-- 
2.26.2

Re: [PATCH hmm v2 2/5] mm/hmm: make hmm_range_fault return 0 or -1

[John Hubbard]

On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> hmm_vma_walk->last is supposed to be updated after every write to the
> pfns, so that it can be returned by hmm_range_fault(). However, this is
> not done consistently. Fortunately nothing checks the return code of
> hmm_range_fault() for anything other than error.
> 
> More importantly last must be set before returning -EBUSY as it is used to
> prevent reading an output pfn as an input flags when the loop restarts.
> 
> For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only
> set last when returning -EBUSY.

Yes, this is also a nice simplification.

> ...
> @@ -590,10 +580,13 @@ long hmm_range_fault(struct hmm_range *range)
>   			return -EBUSY;
>   		ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
>   				      &hmm_walk_ops, &hmm_vma_walk);
> +		/*
> +		 * When -EBUSY is returned the loop restarts with
> +		 * hmm_vma_walk.last set to an address that has not been stored
> +		 * in pfns. All entries < last in the pfn array are set to their
> +		 * output, and all >= are still at their input values.
> +		 */

I'm glad you added that comment. This is much easier to figure out with
that in place. After poking around this patch and eventually understanding the
.last handling, I wondered if you might like this slightly tweaked wording
instead:

		/*
		 * Each of the hmm_walk_ops routines returns -EBUSY if and only
		 * hmm_vma_walk.last has been set to an address that has not yet
		 * been stored in pfns. All entries < last in the pfn array are
		 * set to their output, and all >= are still at their input
		 * values.
		 */

Either way,

     Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA

>   	} while (ret == -EBUSY);
> -
> -	if (ret)
> -		return ret;
> -	return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
> +	return ret;
>   }
>   EXPORT_SYMBOL(hmm_range_fault);
> 

[PATCH hmm v2 3/5] drm/amdgpu: remove dead code after hmm_range_fault()

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

Since amdgpu does not use the snapshot mode of hmm_range_fault() a
successful return already proves that all entries in the pfns are
HMM_PFN_VALID, there is no need to check the return result of
hmm_device_entry_to_page().

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 7eb745b8acce0f..41ae7f96f48194 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -862,17 +862,13 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
 		goto out_free_pfns;
 	}
 
-	for (i = 0; i < ttm->num_pages; i++) {
-		/* FIXME: The pages cannot be touched outside the notifier_lock */
+	/*
+	 * Due to default_flags, all pages are HMM_PFN_VALID or
+	 * hmm_range_fault() fails. FIXME: The pages cannot be touched outside
+	 * the notifier_lock, and mmu_interval_read_retry() must be done first.
+	 */
+	for (i = 0; i < ttm->num_pages; i++)
 		pages[i] = hmm_device_entry_to_page(range, range->pfns[i]);
-		if (unlikely(!pages[i])) {
-			pr_err("Page fault failed for pfn[%lu] = 0x%llx\n",
-			       i, range->pfns[i]);
-			r = -ENOMEM;
-
-			goto out_free_pfns;
-		}
-	}
 
 	gtt->range = range;
 	mmput(mm);
-- 
2.26.2

[PATCH hmm v2 4/5] mm/hmm: remove HMM_PFN_SPECIAL

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

This is just an alias for HMM_PFN_ERROR, nothing cares that the error was
because of a special page vs any other error case.

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 1 -
 drivers/gpu/drm/nouveau/nouveau_svm.c   | 1 -
 include/linux/hmm.h                     | 8 --------
 mm/hmm.c                                | 2 +-
 4 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 41ae7f96f48194..76b4a4fa39ed04 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -775,7 +775,6 @@ static const uint64_t hmm_range_flags[HMM_PFN_FLAG_MAX] = {
 static const uint64_t hmm_range_values[HMM_PFN_VALUE_MAX] = {
 	0xfffffffffffffffeUL, /* HMM_PFN_ERROR */
 	0, /* HMM_PFN_NONE */
-	0xfffffffffffffffcUL /* HMM_PFN_SPECIAL */
 };
 
 /**
diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index c68e9317cf0740..cf0d9bd61bebf9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -379,7 +379,6 @@ static const u64
 nouveau_svm_pfn_values[HMM_PFN_VALUE_MAX] = {
 	[HMM_PFN_ERROR  ] = ~NVIF_VMM_PFNMAP_V0_V,
 	[HMM_PFN_NONE   ] =  NVIF_VMM_PFNMAP_V0_NONE,
-	[HMM_PFN_SPECIAL] = ~NVIF_VMM_PFNMAP_V0_V,
 };
 
 /* Issue fault replay for GPU to retry accesses that faulted previously. */
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 0df27dd03d53d7..81c302c884c0e3 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -44,10 +44,6 @@ enum hmm_pfn_flag_e {
  * Flags:
  * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
  * HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
- * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
- *      result of vmf_insert_pfn() or vm_insert_page(). Therefore, it should not
- *      be mirrored by a device, because the entry will never have HMM_PFN_VALID
- *      set and the pfn value is undefined.
  *
  * Driver provides values for none entry, error entry, and special entry.
  * Driver can alias (i.e., use same value) error and special, but
@@ -56,12 +52,10 @@ enum hmm_pfn_flag_e {
  * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
  * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
  * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry,
- * hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one
  */
 enum hmm_pfn_value_e {
 	HMM_PFN_ERROR,
 	HMM_PFN_NONE,
-	HMM_PFN_SPECIAL,
 	HMM_PFN_VALUE_MAX
 };
 
@@ -110,8 +104,6 @@ static inline struct page *hmm_device_entry_to_page(const struct hmm_range *rang
 		return NULL;
 	if (entry == range->values[HMM_PFN_ERROR])
 		return NULL;
-	if (entry == range->values[HMM_PFN_SPECIAL])
-		return NULL;
 	if (!(entry & range->flags[HMM_PFN_VALID]))
 		return NULL;
 	return pfn_to_page(entry >> range->pfn_shift);
diff --git a/mm/hmm.c b/mm/hmm.c
index f06bcac948a79b..2e975eedb14f89 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -301,7 +301,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 			pte_unmap(ptep);
 			return -EFAULT;
 		}
-		*pfn = range->values[HMM_PFN_SPECIAL];
+		*pfn = range->values[HMM_PFN_ERROR];
 		return 0;
 	}
 
-- 
2.26.2

Re: [PATCH hmm v2 4/5] mm/hmm: remove HMM_PFN_SPECIAL

[John Hubbard]

On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> This is just an alias for HMM_PFN_ERROR, nothing cares that the error was
> because of a special page vs any other error case.

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard
NVIDIA
> 
> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 1 -
>   drivers/gpu/drm/nouveau/nouveau_svm.c   | 1 -
>   include/linux/hmm.h                     | 8 --------
>   mm/hmm.c                                | 2 +-
>   4 files changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 41ae7f96f48194..76b4a4fa39ed04 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -775,7 +775,6 @@ static const uint64_t hmm_range_flags[HMM_PFN_FLAG_MAX] = {
>   static const uint64_t hmm_range_values[HMM_PFN_VALUE_MAX] = {
>   	0xfffffffffffffffeUL, /* HMM_PFN_ERROR */
>   	0, /* HMM_PFN_NONE */
> -	0xfffffffffffffffcUL /* HMM_PFN_SPECIAL */
>   };
>   
>   /**
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index c68e9317cf0740..cf0d9bd61bebf9 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -379,7 +379,6 @@ static const u64
>   nouveau_svm_pfn_values[HMM_PFN_VALUE_MAX] = {
>   	[HMM_PFN_ERROR  ] = ~NVIF_VMM_PFNMAP_V0_V,
>   	[HMM_PFN_NONE   ] =  NVIF_VMM_PFNMAP_V0_NONE,
> -	[HMM_PFN_SPECIAL] = ~NVIF_VMM_PFNMAP_V0_V,
>   };
>   
>   /* Issue fault replay for GPU to retry accesses that faulted previously. */
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 0df27dd03d53d7..81c302c884c0e3 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -44,10 +44,6 @@ enum hmm_pfn_flag_e {
>    * Flags:
>    * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
>    * HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
> - * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
> - *      result of vmf_insert_pfn() or vm_insert_page(). Therefore, it should not
> - *      be mirrored by a device, because the entry will never have HMM_PFN_VALID
> - *      set and the pfn value is undefined.
>    *
>    * Driver provides values for none entry, error entry, and special entry.
>    * Driver can alias (i.e., use same value) error and special, but
> @@ -56,12 +52,10 @@ enum hmm_pfn_flag_e {
>    * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
>    * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
>    * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry,
> - * hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one
>    */
>   enum hmm_pfn_value_e {
>   	HMM_PFN_ERROR,
>   	HMM_PFN_NONE,
> -	HMM_PFN_SPECIAL,
>   	HMM_PFN_VALUE_MAX
>   };
>   
> @@ -110,8 +104,6 @@ static inline struct page *hmm_device_entry_to_page(const struct hmm_range *rang
>   		return NULL;
>   	if (entry == range->values[HMM_PFN_ERROR])
>   		return NULL;
> -	if (entry == range->values[HMM_PFN_SPECIAL])
> -		return NULL;
>   	if (!(entry & range->flags[HMM_PFN_VALID]))
>   		return NULL;
>   	return pfn_to_page(entry >> range->pfn_shift);
> diff --git a/mm/hmm.c b/mm/hmm.c
> index f06bcac948a79b..2e975eedb14f89 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -301,7 +301,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
>   			pte_unmap(ptep);
>   			return -EFAULT;
>   		}
> -		*pfn = range->values[HMM_PFN_SPECIAL];
> +		*pfn = range->values[HMM_PFN_ERROR];
>   		return 0;
>   	}
>   
> 

[PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg@mellanox.com>

Presumably the intent here was that hmm_range_fault() could put the data
into some HW specific format and thus avoid some work. However, nothing
actually does that, and it isn't clear how anything actually could do that
as hmm_range_fault() provides CPU addresses which must be DMA mapped.

Perhaps there is some special HW that does not need DMA mapping, but we
don't have any examples of this, and the theoretical performance win of
avoiding an extra scan over the pfns array doesn't seem worth the
complexity. Plus pfns needs to be scanned anyhow to sort out any
DEVICE_PRIVATE pages.

This version replaces the uint64_t with an usigned long containing a pfn
and fixed flags. On input flags is filled with the HMM_PFN_REQ_* values,
on successful output it is filled with HMM_PFN_* values, describing the
state of the pages.

amdgpu is simple to convert, it doesn't use snapshot and doesn't use
per-page flags.

nouveau uses only 16 hmm_pte entries at most (ie fits in a few cache
lines), and it sweeps over its pfns array a couple of times anyhow. It
also has a nasty call chain before it reaches the dma map and hardware
suggesting performance isn't important:

   nouveau_svm_fault():
     args.i.m.method = NVIF_VMM_V0_PFNMAP
     nouveau_range_fault()
      nvif_object_ioctl()
       client->driver->ioctl()
	  struct nvif_driver nvif_driver_nvkm:
	    .ioctl = nvkm_client_ioctl
	   nvkm_ioctl()
	    nvkm_ioctl_path()
	      nvkm_ioctl_v0[type].func(..)
	      nvkm_ioctl_mthd()
	       nvkm_object_mthd()
		  struct nvkm_object_func nvkm_uvmm:
		    .mthd = nvkm_uvmm_mthd
		   nvkm_uvmm_mthd()
		    nvkm_uvmm_mthd_pfnmap()
		     nvkm_vmm_pfn_map()
		      nvkm_vmm_ptes_get_map()
		       func == gp100_vmm_pgt_pfn
			struct nvkm_vmm_desc_func gp100_vmm_desc_spt:
			  .pfn = gp100_vmm_pgt_pfn
			 nvkm_vmm_iter()
			  REF_PTES == func == gp100_vmm_pgt_pfn()
			    dma_map_page()

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/vm/hmm.rst                |  26 ++--
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  35 ++----
 drivers/gpu/drm/nouveau/nouveau_dmem.c  |  27 +---
 drivers/gpu/drm/nouveau/nouveau_dmem.h  |   3 +-
 drivers/gpu/drm/nouveau/nouveau_svm.c   |  87 ++++++++-----
 include/linux/hmm.h                     |  99 ++++++---------
 mm/hmm.c                                | 160 +++++++++++-------------
 7 files changed, 192 insertions(+), 245 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 9924f2caa0184c..c9f2329113a47f 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -185,9 +185,6 @@ The usage pattern is::
       range.start = ...;
       range.end = ...;
       range.pfns = ...;
-      range.flags = ...;
-      range.values = ...;
-      range.pfn_shift = ...;
 
       if (!mmget_not_zero(interval_sub->notifier.mm))
           return -EFAULT;
@@ -229,15 +226,10 @@ The hmm_range struct has 2 fields, default_flags and pfn_flags_mask, that specif
 fault or snapshot policy for the whole range instead of having to set them
 for each entry in the pfns array.
 
-For instance, if the device flags for range.flags are::
+For instance if the device driver wants pages for a range with at least read
+permission, it sets::
 
-    range.flags[HMM_PFN_VALID] = (1 << 63);
-    range.flags[HMM_PFN_WRITE] = (1 << 62);
-
-and the device driver wants pages for a range with at least read permission,
-it sets::
-
-    range->default_flags = (1 << 63);
+    range->default_flags = HMM_PFN_REQ_FAULT;
     range->pfn_flags_mask = 0;
 
 and calls hmm_range_fault() as described above. This will fill fault all pages
@@ -246,18 +238,18 @@ in the range with at least read permission.
 Now let's say the driver wants to do the same except for one page in the range for
 which it wants to have write permission. Now driver set::
 
-    range->default_flags = (1 << 63);
-    range->pfn_flags_mask = (1 << 62);
-    range->pfns[index_of_write] = (1 << 62);
+    range->default_flags = HMM_PFN_REQ_FAULT;
+    range->pfn_flags_mask = HMM_PFN_REQ_WRITE;
+    range->pfns[index_of_write] = HMM_PFN_REQ_WRITE;
 
 With this, HMM will fault in all pages with at least read (i.e., valid) and for the
 address == range->start + (index_of_write << PAGE_SHIFT) it will fault with
 write permission i.e., if the CPU pte does not have write permission set then HMM
 will call handle_mm_fault().
 
-Note that HMM will populate the pfns array with write permission for any page
-that is mapped with CPU write permission no matter what values are set
-in default_flags or pfn_flags_mask.
+After hmm_range_fault completes the flag bits are set to the current state of
+the page tables, ie HMM_PFN_VALID | HMM_PFN_WRITE will be set if the page is
+writable.
 
 
 Represent and manage device memory from core kernel point of view
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 76b4a4fa39ed04..b1c62da527c59b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -766,17 +766,6 @@ struct amdgpu_ttm_tt {
 };
 
 #ifdef CONFIG_DRM_AMDGPU_USERPTR
-/* flags used by HMM internal, not related to CPU/GPU PTE flags */
-static const uint64_t hmm_range_flags[HMM_PFN_FLAG_MAX] = {
-	(1 << 0), /* HMM_PFN_VALID */
-	(1 << 1), /* HMM_PFN_WRITE */
-};
-
-static const uint64_t hmm_range_values[HMM_PFN_VALUE_MAX] = {
-	0xfffffffffffffffeUL, /* HMM_PFN_ERROR */
-	0, /* HMM_PFN_NONE */
-};
-
 /**
  * amdgpu_ttm_tt_get_user_pages - get device accessible pages that back user
  * memory and start HMM tracking CPU page table update
@@ -815,18 +804,15 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
 		goto out;
 	}
 	range->notifier = &bo->notifier;
-	range->flags = hmm_range_flags;
-	range->values = hmm_range_values;
-	range->pfn_shift = PAGE_SHIFT;
 	range->start = bo->notifier.interval_tree.start;
 	range->end = bo->notifier.interval_tree.last + 1;
-	range->default_flags = hmm_range_flags[HMM_PFN_VALID];
+	range->default_flags = HMM_PFN_REQ_FAULT;
 	if (!amdgpu_ttm_tt_is_readonly(ttm))
-		range->default_flags |= range->flags[HMM_PFN_WRITE];
+		range->default_flags |= HMM_PFN_REQ_WRITE;
 
-	range->pfns = kvmalloc_array(ttm->num_pages, sizeof(*range->pfns),
-				     GFP_KERNEL);
-	if (unlikely(!range->pfns)) {
+	range->hmm_pfns = kvmalloc_array(ttm->num_pages,
+					 sizeof(*range->hmm_pfns), GFP_KERNEL);
+	if (unlikely(!range->hmm_pfns)) {
 		r = -ENOMEM;
 		goto out_free_ranges;
 	}
@@ -867,7 +853,7 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
 	 * the notifier_lock, and mmu_interval_read_retry() must be done first.
 	 */
 	for (i = 0; i < ttm->num_pages; i++)
-		pages[i] = hmm_device_entry_to_page(range, range->pfns[i]);
+		pages[i] = hmm_pfn_to_page(range->hmm_pfns[i]);
 
 	gtt->range = range;
 	mmput(mm);
@@ -877,7 +863,7 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
 out_unlock:
 	up_read(&mm->mmap_sem);
 out_free_pfns:
-	kvfree(range->pfns);
+	kvfree(range->hmm_pfns);
 out_free_ranges:
 	kfree(range);
 out:
@@ -902,7 +888,7 @@ bool amdgpu_ttm_tt_get_user_pages_done(struct ttm_tt *ttm)
 	DRM_DEBUG_DRIVER("user_pages_done 0x%llx pages 0x%lx\n",
 		gtt->userptr, ttm->num_pages);
 
-	WARN_ONCE(!gtt->range || !gtt->range->pfns,
+	WARN_ONCE(!gtt->range || !gtt->range->hmm_pfns,
 		"No user pages to check\n");
 
 	if (gtt->range) {
@@ -912,7 +898,7 @@ bool amdgpu_ttm_tt_get_user_pages_done(struct ttm_tt *ttm)
 		 */
 		r = mmu_interval_read_retry(gtt->range->notifier,
 					 gtt->range->notifier_seq);
-		kvfree(gtt->range->pfns);
+		kvfree(gtt->range->hmm_pfns);
 		kfree(gtt->range);
 		gtt->range = NULL;
 	}
@@ -1003,8 +989,7 @@ static void amdgpu_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
 
 		for (i = 0; i < ttm->num_pages; i++) {
 			if (ttm->pages[i] !=
-				hmm_device_entry_to_page(gtt->range,
-					      gtt->range->pfns[i]))
+			    hmm_pfn_to_page(gtt->range->hmm_pfns[i]))
 				break;
 		}
 
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index ad89e09a0be39a..3364904eccff5a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -85,7 +85,7 @@ static inline struct nouveau_dmem *page_to_dmem(struct page *page)
 	return container_of(page->pgmap, struct nouveau_dmem, pagemap);
 }
 
-static unsigned long nouveau_dmem_page_addr(struct page *page)
+unsigned long nouveau_dmem_page_addr(struct page *page)
 {
 	struct nouveau_dmem_chunk *chunk = page->zone_device_data;
 	unsigned long idx = page_to_pfn(page) - chunk->pfn_first;
@@ -671,28 +671,3 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 out:
 	return ret;
 }
-
-void
-nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
-			 struct hmm_range *range)
-{
-	unsigned long i, npages;
-
-	npages = (range->end - range->start) >> PAGE_SHIFT;
-	for (i = 0; i < npages; ++i) {
-		struct page *page;
-		uint64_t addr;
-
-		page = hmm_device_entry_to_page(range, range->pfns[i]);
-		if (page == NULL)
-			continue;
-
-		if (!is_device_private_page(page))
-			continue;
-
-		addr = nouveau_dmem_page_addr(page);
-		range->pfns[i] &= ((1UL << range->pfn_shift) - 1);
-		range->pfns[i] |= (addr >> PAGE_SHIFT) << range->pfn_shift;
-		range->pfns[i] |= NVIF_VMM_PFNMAP_V0_VRAM;
-	}
-}
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.h b/drivers/gpu/drm/nouveau/nouveau_dmem.h
index 92394be5d64923..db3b59b210af13 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.h
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.h
@@ -37,9 +37,8 @@ int nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 			     struct vm_area_struct *vma,
 			     unsigned long start,
 			     unsigned long end);
+unsigned long nouveau_dmem_page_addr(struct page *page);
 
-void nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
-			      struct hmm_range *range);
 #else /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
 static inline void nouveau_dmem_init(struct nouveau_drm *drm) {}
 static inline void nouveau_dmem_fini(struct nouveau_drm *drm) {}
diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index cf0d9bd61bebf9..99697df28bfe12 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -369,18 +369,6 @@ nouveau_svmm_init(struct drm_device *dev, void *data,
 	return ret;
 }
 
-static const u64
-nouveau_svm_pfn_flags[HMM_PFN_FLAG_MAX] = {
-	[HMM_PFN_VALID         ] = NVIF_VMM_PFNMAP_V0_V,
-	[HMM_PFN_WRITE         ] = NVIF_VMM_PFNMAP_V0_W,
-};
-
-static const u64
-nouveau_svm_pfn_values[HMM_PFN_VALUE_MAX] = {
-	[HMM_PFN_ERROR  ] = ~NVIF_VMM_PFNMAP_V0_V,
-	[HMM_PFN_NONE   ] =  NVIF_VMM_PFNMAP_V0_NONE,
-};
-
 /* Issue fault replay for GPU to retry accesses that faulted previously. */
 static void
 nouveau_svm_fault_replay(struct nouveau_svm *svm)
@@ -518,9 +506,45 @@ static const struct mmu_interval_notifier_ops nouveau_svm_mni_ops = {
 	.invalidate = nouveau_svm_range_invalidate,
 };
 
+static void nouveau_hmm_convert_pfn(struct nouveau_drm *drm,
+				    struct hmm_range *range, u64 *ioctl_addr)
+{
+	unsigned long i, npages;
+
+	/*
+	 * The ioctl_addr prepared here is passed through nvif_object_ioctl()
+	 * to an eventual DMA map in something like gp100_vmm_pgt_pfn()
+	 *
+	 * This is all just encoding the internal hmm reprensetation into a
+	 * different nouveau internal representation.
+	 */
+	npages = (range->end - range->start) >> PAGE_SHIFT;
+	for (i = 0; i < npages; ++i) {
+		struct page *page;
+
+		if (!(range->hmm_pfns[i] & HMM_PFN_VALID)) {
+			ioctl_addr[i] = 0;
+			continue;
+		}
+
+		page = hmm_pfn_to_page(range->hmm_pfns[i]);
+		if (is_device_private_page(page))
+			ioctl_addr[i] = nouveau_dmem_page_addr(page) |
+					NVIF_VMM_PFNMAP_V0_V |
+					NVIF_VMM_PFNMAP_V0_VRAM;
+		else
+			ioctl_addr[i] = page_to_phys(page) |
+					NVIF_VMM_PFNMAP_V0_V |
+					NVIF_VMM_PFNMAP_V0_HOST;
+		if (range->hmm_pfns[i] & HMM_PFN_WRITE)
+			ioctl_addr[i] |= NVIF_VMM_PFNMAP_V0_W;
+	}
+}
+
 static int nouveau_range_fault(struct nouveau_svmm *svmm,
 			       struct nouveau_drm *drm, void *data, u32 size,
-			       u64 *pfns, struct svm_notifier *notifier)
+			       unsigned long hmm_pfns[], u64 *ioctl_addr,
+			       struct svm_notifier *notifier)
 {
 	unsigned long timeout =
 		jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
@@ -529,10 +553,8 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 		.notifier = &notifier->notifier,
 		.start = notifier->notifier.interval_tree.start,
 		.end = notifier->notifier.interval_tree.last + 1,
-		.pfns = pfns,
-		.flags = nouveau_svm_pfn_flags,
-		.values = nouveau_svm_pfn_values,
-		.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT,
+		.pfn_flags_mask = HMM_PFN_REQ_FAULT | HMM_PFN_REQ_WRITE,
+		.hmm_pfns = hmm_pfns,
 	};
 	struct mm_struct *mm = notifier->notifier.mm;
 	int ret;
@@ -542,12 +564,15 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 			return -EBUSY;
 
 		range.notifier_seq = mmu_interval_read_begin(range.notifier);
-		range.default_flags = 0;
-		range.pfn_flags_mask = -1UL;
 		down_read(&mm->mmap_sem);
 		ret = hmm_range_fault(&range);
 		up_read(&mm->mmap_sem);
 		if (ret) {
+			/*
+			 * FIXME: the input PFN_REQ flags are destroyed on
+			 * -EBUSY, we need to regenerate them, also for the
+			 * other continue below
+			 */
 			if (ret == -EBUSY)
 				continue;
 			return ret;
@@ -562,7 +587,7 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 		break;
 	}
 
-	nouveau_dmem_convert_pfn(drm, &range);
+	nouveau_hmm_convert_pfn(drm, &range, ioctl_addr);
 
 	svmm->vmm->vmm.object.client->super = true;
 	ret = nvif_object_ioctl(&svmm->vmm->vmm.object, data, size, NULL);
@@ -589,6 +614,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
 		} i;
 		u64 phys[16];
 	} args;
+	unsigned long hmm_pfns[ARRAY_SIZE(args.phys)];
 	struct vm_area_struct *vma;
 	u64 inst, start, limit;
 	int fi, fn, pi, fill;
@@ -704,12 +730,17 @@ nouveau_svm_fault(struct nvif_notify *notify)
 			 * access flags.
 			 *XXX: atomic?
 			 */
-			if (buffer->fault[fn]->access != 0 /* READ. */ &&
-			    buffer->fault[fn]->access != 3 /* PREFETCH. */) {
-				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_V |
-						  NVIF_VMM_PFNMAP_V0_W;
-			} else {
-				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_V;
+			switch (buffer->fault[fn]->access) {
+			case 0: /* READ. */
+				hmm_pfns[pi++] = HMM_PFN_REQ_FAULT;
+				break;
+			case 3: /* PREFETCH. */
+				hmm_pfns[pi++] = 0;
+				break;
+			default:
+				hmm_pfns[pi++] = HMM_PFN_REQ_FAULT |
+						 HMM_PFN_REQ_WRITE;
+				break;
 			}
 			args.i.p.size = pi << PAGE_SHIFT;
 
@@ -737,7 +768,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
 			fill = (buffer->fault[fn    ]->addr -
 				buffer->fault[fn - 1]->addr) >> PAGE_SHIFT;
 			while (--fill)
-				args.phys[pi++] = NVIF_VMM_PFNMAP_V0_NONE;
+				hmm_pfns[pi++] = 0;
 		}
 
 		SVMM_DBG(svmm, "wndw %016llx-%016llx covering %d fault(s)",
@@ -753,7 +784,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
 			ret = nouveau_range_fault(
 				svmm, svm->drm, &args,
 				sizeof(args.i) + pi * sizeof(args.phys[0]),
-				args.phys, &notifier);
+				hmm_pfns, args.phys, &notifier);
 			mmu_interval_notifier_remove(&notifier.notifier);
 		}
 		mmput(mm);
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 81c302c884c0e3..e72529786f16f8 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -19,45 +19,45 @@
 #include <linux/mmu_notifier.h>
 
 /*
- * hmm_pfn_flag_e - HMM flag enums
+ * On output:
+ * 0             - The page is faultable and a future call with 
+ *                 HMM_PFN_REQ_FAULT could succeed.
+ * HMM_PFN_VALID - the pfn field points to a valid PFN. This PFN is at
+ *                 least readable. If dev_private_owner is !NULL then this could
+ *                 point at a DEVICE_PRIVATE page.
+ * HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
+ * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
+ *                 fail. ie poisoned memory, special pages, no vma, etc
  *
- * Flags:
- * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
- * HMM_PFN_WRITE: CPU page table has write permission set
- *
- * The driver provides a flags array for mapping page protections to device
- * PTE bits. If the driver valid bit for an entry is bit 3,
- * i.e., (entry & (1 << 3)), then the driver must provide
- * an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3.
- * Same logic apply to all flags. This is the same idea as vm_page_prot in vma
- * except that this is per device driver rather than per architecture.
+ * On input:
+ * 0                 - Return the current state of the page, do not fault it.
+ * HMM_PFN_REQ_FAULT - The output must have HMM_PFN_VALID or hmm_range_fault()
+ *                     will fail
+ * HMM_PFN_REQ_WRITE - The output must have HMM_PFN_WRITE or hmm_range_fault()
+ *                     will fail. Must be combined with HMM_PFN_REQ_FAULT.
  */
-enum hmm_pfn_flag_e {
-	HMM_PFN_VALID = 0,
-	HMM_PFN_WRITE,
-	HMM_PFN_FLAG_MAX
+enum hmm_pfn_flags {
+	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
+	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
+	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
+
+	HMM_PFN_REQ_FAULT = HMM_PFN_VALID,
+	HMM_PFN_REQ_WRITE = HMM_PFN_WRITE,
+
+	HMM_PFN_FLAGS = HMM_PFN_VALID | HMM_PFN_WRITE | HMM_PFN_ERROR,
 };
 
 /*
- * hmm_pfn_value_e - HMM pfn special value
- *
- * Flags:
- * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
- * HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
+ * hmm_pfn_to_page() - return struct page pointed to by a device entry
  *
- * Driver provides values for none entry, error entry, and special entry.
- * Driver can alias (i.e., use same value) error and special, but
- * it should not alias none with error or special.
- *
- * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
- * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
- * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry,
+ * This must be called under the caller 'user_lock' after a successful
+ * mmu_interval_read_begin(). The caller must have tested for HMM_PFN_VALID
+ * already.
  */
-enum hmm_pfn_value_e {
-	HMM_PFN_ERROR,
-	HMM_PFN_NONE,
-	HMM_PFN_VALUE_MAX
-};
+static inline struct page *hmm_pfn_to_page(unsigned long hmm_pfn)
+{
+	return pfn_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
+}
 
 /*
  * struct hmm_range - track invalidation lock on virtual address range
@@ -66,12 +66,9 @@ enum hmm_pfn_value_e {
  * @notifier_seq: result of mmu_interval_read_begin()
  * @start: range virtual start address (inclusive)
  * @end: range virtual end address (exclusive)
- * @pfns: array of pfns (big enough for the range)
- * @flags: pfn flags to match device driver page table
- * @values: pfn value for some special case (none, special, error, ...)
+ * @hmm_pfns: array of pfns (big enough for the range)
  * @default_flags: default flags for the range (write, read, ... see hmm doc)
  * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
- * @pfn_shift: pfn shift value (should be <= PAGE_SHIFT)
  * @dev_private_owner: owner of device private pages
  */
 struct hmm_range {
@@ -79,36 +76,12 @@ struct hmm_range {
 	unsigned long		notifier_seq;
 	unsigned long		start;
 	unsigned long		end;
-	uint64_t		*pfns;
-	const uint64_t		*flags;
-	const uint64_t		*values;
-	uint64_t		default_flags;
-	uint64_t		pfn_flags_mask;
-	uint8_t			pfn_shift;
+	unsigned long		*hmm_pfns;
+	unsigned long		default_flags;
+	unsigned long		pfn_flags_mask;
 	void			*dev_private_owner;
 };
 
-/*
- * hmm_device_entry_to_page() - return struct page pointed to by a device entry
- * @range: range use to decode device entry value
- * @entry: device entry value to get corresponding struct page from
- * Return: struct page pointer if entry is a valid, NULL otherwise
- *
- * If the device entry is valid (ie valid flag set) then return the struct page
- * matching the entry value. Otherwise return NULL.
- */
-static inline struct page *hmm_device_entry_to_page(const struct hmm_range *range,
-						    uint64_t entry)
-{
-	if (entry == range->values[HMM_PFN_NONE])
-		return NULL;
-	if (entry == range->values[HMM_PFN_ERROR])
-		return NULL;
-	if (!(entry & range->flags[HMM_PFN_VALID]))
-		return NULL;
-	return pfn_to_page(entry >> range->pfn_shift);
-}
-
 /*
  * Please see Documentation/vm/hmm.rst for how to use the range API.
  */
diff --git a/mm/hmm.c b/mm/hmm.c
index 2e975eedb14f89..41673a6d8d46d1 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -37,28 +37,13 @@ enum {
 	HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
 };
 
-/*
- * hmm_device_entry_from_pfn() - create a valid device entry value from pfn
- * @range: range use to encode HMM pfn value
- * @pfn: pfn value for which to create the device entry
- * Return: valid device entry for the pfn
- */
-static uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
-					  unsigned long pfn)
-{
-	return (pfn << range->pfn_shift) | range->flags[HMM_PFN_VALID];
-}
-
 static int hmm_pfns_fill(unsigned long addr, unsigned long end,
-		struct hmm_range *range, enum hmm_pfn_value_e value)
+			 struct hmm_range *range, unsigned long cpu_flags)
 {
-	uint64_t *pfns = range->pfns;
-	unsigned long i;
+	unsigned long i = (addr - range->start) >> PAGE_SHIFT;
 
-	i = (addr - range->start) >> PAGE_SHIFT;
 	for (; addr < end; addr += PAGE_SIZE, i++)
-		pfns[i] = range->values[value];
-
+		range->hmm_pfns[i] = cpu_flags;
 	return 0;
 }
 
@@ -96,7 +81,8 @@ static int hmm_vma_fault(unsigned long addr, unsigned long end,
 }
 
 static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
-				       uint64_t pfns, uint64_t cpu_flags)
+				       unsigned long pfn_req_flags,
+				       unsigned long cpu_flags)
 {
 	struct hmm_range *range = hmm_vma_walk->range;
 
@@ -110,27 +96,28 @@ static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 	 * waste to have the user pre-fill the pfn arrays with a default
 	 * flags value.
 	 */
-	pfns = (pfns & range->pfn_flags_mask) | range->default_flags;
+	pfn_req_flags &= range->pfn_flags_mask;
+	pfn_req_flags |= range->default_flags;
 
 	/* We aren't ask to do anything ... */
-	if (!(pfns & range->flags[HMM_PFN_VALID]))
+	if (!(pfn_req_flags & HMM_PFN_REQ_FAULT))
 		return 0;
 
 	/* Need to write fault ? */
-	if ((pfns & range->flags[HMM_PFN_WRITE]) &&
-	    !(cpu_flags & range->flags[HMM_PFN_WRITE]))
+	if ((pfn_req_flags & HMM_PFN_REQ_WRITE) &&
+	    !(cpu_flags & HMM_PFN_WRITE))
 		return HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT;
 
 	/* If CPU page table is not valid then we need to fault */
-	if (!(cpu_flags & range->flags[HMM_PFN_VALID]))
+	if (!(cpu_flags & HMM_PFN_VALID))
 		return HMM_NEED_FAULT;
 	return 0;
 }
 
 static unsigned int
 hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
-		     const uint64_t *pfns, unsigned long npages,
-		     uint64_t cpu_flags)
+		     const unsigned long hmm_pfns[], unsigned long npages,
+		     unsigned long cpu_flags)
 {
 	struct hmm_range *range = hmm_vma_walk->range;
 	unsigned int required_fault = 0;
@@ -142,12 +129,12 @@ hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 	 * hmm_pte_need_fault() will always return 0.
 	 */
 	if (!((range->default_flags | range->pfn_flags_mask) &
-	      range->flags[HMM_PFN_VALID]))
+	      HMM_PFN_REQ_FAULT))
 		return 0;
 
 	for (i = 0; i < npages; ++i) {
-		required_fault |=
-			hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags);
+		required_fault |= hmm_pte_need_fault(hmm_vma_walk, hmm_pfns[i],
+						     cpu_flags);
 		if (required_fault == HMM_NEED_ALL_BITS)
 			return required_fault;
 	}
@@ -161,12 +148,13 @@ static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
 	struct hmm_range *range = hmm_vma_walk->range;
 	unsigned int required_fault;
 	unsigned long i, npages;
-	uint64_t *pfns;
+	unsigned long *hmm_pfns;
 
 	i = (addr - range->start) >> PAGE_SHIFT;
 	npages = (end - addr) >> PAGE_SHIFT;
-	pfns = &range->pfns[i];
-	required_fault = hmm_range_need_fault(hmm_vma_walk, pfns, npages, 0);
+	hmm_pfns = &range->hmm_pfns[i];
+	required_fault =
+		hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0);
 	if (!walk->vma) {
 		if (required_fault)
 			return -EFAULT;
@@ -174,44 +162,44 @@ static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
 	}
 	if (required_fault)
 		return hmm_vma_fault(addr, end, required_fault, walk);
-	return hmm_pfns_fill(addr, end, range, HMM_PFN_NONE);
+	return hmm_pfns_fill(addr, end, range, 0);
 }
 
-static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
+static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
+						 pmd_t pmd)
 {
 	if (pmd_protnone(pmd))
 		return 0;
-	return pmd_write(pmd) ? range->flags[HMM_PFN_VALID] |
-				range->flags[HMM_PFN_WRITE] :
-				range->flags[HMM_PFN_VALID];
+	return pmd_write(pmd) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
-		unsigned long end, uint64_t *pfns, pmd_t pmd)
+			      unsigned long end, unsigned long hmm_pfns[],
+			      pmd_t pmd)
 {
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
 	struct hmm_range *range = hmm_vma_walk->range;
 	unsigned long pfn, npages, i;
 	unsigned int required_fault;
-	uint64_t cpu_flags;
+	unsigned long cpu_flags;
 
 	npages = (end - addr) >> PAGE_SHIFT;
 	cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
 	required_fault =
-		hmm_range_need_fault(hmm_vma_walk, pfns, npages, cpu_flags);
+		hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, cpu_flags);
 	if (required_fault)
 		return hmm_vma_fault(addr, end, required_fault, walk);
 
 	pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
-		pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags;
+		hmm_pfns[i] = pfn | cpu_flags;
 	return 0;
 }
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 /* stub to allow the code below to compile */
 int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
-		unsigned long end, uint64_t *pfns, pmd_t pmd);
+		unsigned long end, unsigned long hmm_pfns[], pmd_t pmd);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 static inline bool hmm_is_device_private_entry(struct hmm_range *range,
@@ -222,31 +210,31 @@ static inline bool hmm_is_device_private_entry(struct hmm_range *range,
 		range->dev_private_owner;
 }
 
-static inline uint64_t pte_to_hmm_pfn_flags(struct hmm_range *range, pte_t pte)
+static inline unsigned long pte_to_hmm_pfn_flags(struct hmm_range *range,
+						 pte_t pte)
 {
 	if (pte_none(pte) || !pte_present(pte) || pte_protnone(pte))
 		return 0;
-	return pte_write(pte) ? range->flags[HMM_PFN_VALID] |
-				range->flags[HMM_PFN_WRITE] :
-				range->flags[HMM_PFN_VALID];
+	return pte_write(pte) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
 }
 
 static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 			      unsigned long end, pmd_t *pmdp, pte_t *ptep,
-			      uint64_t *pfn)
+			      unsigned long *hmm_pfn)
 {
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
 	struct hmm_range *range = hmm_vma_walk->range;
 	unsigned int required_fault;
-	uint64_t cpu_flags;
+	unsigned long cpu_flags;
 	pte_t pte = *ptep;
-	uint64_t orig_pfn = *pfn;
+	uint64_t pfn_req_flags = *hmm_pfn;
 
 	if (pte_none(pte)) {
-		required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0);
+		required_fault =
+			hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
 		if (required_fault)
 			goto fault;
-		*pfn = range->values[HMM_PFN_NONE];
+		*hmm_pfn = 0;
 		return 0;
 	}
 
@@ -258,17 +246,18 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 		 * the PFN even if not present.
 		 */
 		if (hmm_is_device_private_entry(range, entry)) {
-			*pfn = hmm_device_entry_from_pfn(range,
-				device_private_entry_to_pfn(entry));
-			*pfn |= range->flags[HMM_PFN_VALID];
+			cpu_flags = HMM_PFN_VALID;
 			if (is_write_device_private_entry(entry))
-				*pfn |= range->flags[HMM_PFN_WRITE];
+				cpu_flags |= HMM_PFN_WRITE;
+			*hmm_pfn = device_private_entry_to_pfn(entry) |
+					cpu_flags;
 			return 0;
 		}
 
-		required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0);
+		required_fault =
+			hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
 		if (!required_fault) {
-			*pfn = range->values[HMM_PFN_NONE];
+			*hmm_pfn = 0;
 			return 0;
 		}
 
@@ -288,7 +277,8 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 	}
 
 	cpu_flags = pte_to_hmm_pfn_flags(range, pte);
-	required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags);
+	required_fault =
+		hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
 	if (required_fault)
 		goto fault;
 
@@ -297,15 +287,15 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 	 * fall through and treat it like a normal page.
 	 */
 	if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) {
-		if (hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0)) {
+		if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
 			pte_unmap(ptep);
 			return -EFAULT;
 		}
-		*pfn = range->values[HMM_PFN_ERROR];
+		*hmm_pfn = HMM_PFN_ERROR;
 		return 0;
 	}
 
-	*pfn = hmm_device_entry_from_pfn(range, pte_pfn(pte)) | cpu_flags;
+	*hmm_pfn = pte_pfn(pte) | cpu_flags;
 	return 0;
 
 fault:
@@ -321,7 +311,8 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 {
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
 	struct hmm_range *range = hmm_vma_walk->range;
-	uint64_t *pfns = &range->pfns[(start - range->start) >> PAGE_SHIFT];
+	unsigned long *hmm_pfns =
+		&range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
 	unsigned long npages = (end - start) >> PAGE_SHIFT;
 	unsigned long addr = start;
 	pte_t *ptep;
@@ -333,16 +324,16 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 		return hmm_vma_walk_hole(start, end, -1, walk);
 
 	if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
-		if (hmm_range_need_fault(hmm_vma_walk, pfns, npages, 0)) {
+		if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
 			hmm_vma_walk->last = addr;
 			pmd_migration_entry_wait(walk->mm, pmdp);
 			return -EBUSY;
 		}
-		return hmm_pfns_fill(start, end, range, HMM_PFN_NONE);
+		return hmm_pfns_fill(start, end, range, 0);
 	}
 
 	if (!pmd_present(pmd)) {
-		if (hmm_range_need_fault(hmm_vma_walk, pfns, npages, 0))
+		if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 			return -EFAULT;
 		return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 	}
@@ -362,7 +353,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 		if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 			goto again;
 
-		return hmm_vma_handle_pmd(walk, addr, end, pfns, pmd);
+		return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
 	}
 
 	/*
@@ -372,16 +363,16 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 	 * recover.
 	 */
 	if (pmd_bad(pmd)) {
-		if (hmm_range_need_fault(hmm_vma_walk, pfns, npages, 0))
+		if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 			return -EFAULT;
 		return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 	}
 
 	ptep = pte_offset_map(pmdp, addr);
-	for (; addr < end; addr += PAGE_SIZE, ptep++, pfns++) {
+	for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
 		int r;
 
-		r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, pfns);
+		r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
 		if (r) {
 			/* hmm_vma_handle_pte() did pte_unmap() */
 			return r;
@@ -393,13 +384,12 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 
 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
     defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
-static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
+static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
+						 pud_t pud)
 {
 	if (!pud_present(pud))
 		return 0;
-	return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
-				range->flags[HMM_PFN_WRITE] :
-				range->flags[HMM_PFN_VALID];
+	return pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
 }
 
 static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
@@ -427,7 +417,8 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 	if (pud_huge(pud) && pud_devmap(pud)) {
 		unsigned long i, npages, pfn;
 		unsigned int required_fault;
-		uint64_t *pfns, cpu_flags;
+		unsigned long *hmm_pfns;
+		unsigned long cpu_flags;
 
 		if (!pud_present(pud)) {
 			spin_unlock(ptl);
@@ -436,10 +427,10 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 
 		i = (addr - range->start) >> PAGE_SHIFT;
 		npages = (end - addr) >> PAGE_SHIFT;
-		pfns = &range->pfns[i];
+		hmm_pfns = &range->hmm_pfns[i];
 
 		cpu_flags = pud_to_hmm_pfn_flags(range, pud);
-		required_fault = hmm_range_need_fault(hmm_vma_walk, pfns,
+		required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
 						      npages, cpu_flags);
 		if (required_fault) {
 			spin_unlock(ptl);
@@ -448,8 +439,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 
 		pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 		for (i = 0; i < npages; ++i, ++pfn)
-			pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
-				  cpu_flags;
+			hmm_pfns[i] = pfn | cpu_flags;
 		goto out_unlock;
 	}
 
@@ -473,8 +463,9 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
 	struct hmm_range *range = hmm_vma_walk->range;
 	struct vm_area_struct *vma = walk->vma;
-	uint64_t orig_pfn, cpu_flags;
 	unsigned int required_fault;
+	unsigned long pfn_req_flags;
+	unsigned long cpu_flags;
 	spinlock_t *ptl;
 	pte_t entry;
 
@@ -482,9 +473,10 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 	entry = huge_ptep_get(pte);
 
 	i = (start - range->start) >> PAGE_SHIFT;
-	orig_pfn = range->pfns[i];
+	pfn_req_flags = range->hmm_pfns[i];
 	cpu_flags = pte_to_hmm_pfn_flags(range, entry);
-	required_fault = hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags);
+	required_fault =
+		hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
 	if (required_fault) {
 		spin_unlock(ptl);
 		return hmm_vma_fault(addr, end, required_fault, walk);
@@ -492,8 +484,8 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 
 	pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
 	for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
-		range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
-				 cpu_flags;
+		range->hmm_pfns[i] = pfn | cpu_flags;
+
 	spin_unlock(ptl);
 	return 0;
 }
@@ -524,7 +516,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end,
 	 * failure.
 	 */
 	if (hmm_range_need_fault(hmm_vma_walk,
-				 range->pfns +
+				 range->hmm_pfns +
 					 ((start - range->start) >> PAGE_SHIFT),
 				 (end - start) >> PAGE_SHIFT, 0))
 		return -EFAULT;
-- 
2.26.2

Re: [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[Ralph Campbell]

On 5/1/20 11:20 AM, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> Presumably the intent here was that hmm_range_fault() could put the data
> into some HW specific format and thus avoid some work. However, nothing
> actually does that, and it isn't clear how anything actually could do that
> as hmm_range_fault() provides CPU addresses which must be DMA mapped.
> 
> Perhaps there is some special HW that does not need DMA mapping, but we
> don't have any examples of this, and the theoretical performance win of
> avoiding an extra scan over the pfns array doesn't seem worth the
> complexity. Plus pfns needs to be scanned anyhow to sort out any
> DEVICE_PRIVATE pages.
> 
> This version replaces the uint64_t with an usigned long containing a pfn
> and fixed flags. On input flags is filled with the HMM_PFN_REQ_* values,
> on successful output it is filled with HMM_PFN_* values, describing the
> state of the pages.
> 
> amdgpu is simple to convert, it doesn't use snapshot and doesn't use
> per-page flags.
> 
> nouveau uses only 16 hmm_pte entries at most (ie fits in a few cache
> lines), and it sweeps over its pfns array a couple of times anyhow. It
> also has a nasty call chain before it reaches the dma map and hardware
> suggesting performance isn't important:
> 
>     nouveau_svm_fault():
>       args.i.m.method = NVIF_VMM_V0_PFNMAP
>       nouveau_range_fault()
>        nvif_object_ioctl()
>         client->driver->ioctl()
> 	  struct nvif_driver nvif_driver_nvkm:
> 	    .ioctl = nvkm_client_ioctl
> 	   nvkm_ioctl()
> 	    nvkm_ioctl_path()
> 	      nvkm_ioctl_v0[type].func(..)
> 	      nvkm_ioctl_mthd()
> 	       nvkm_object_mthd()
> 		  struct nvkm_object_func nvkm_uvmm:
> 		    .mthd = nvkm_uvmm_mthd
> 		   nvkm_uvmm_mthd()
> 		    nvkm_uvmm_mthd_pfnmap()
> 		     nvkm_vmm_pfn_map()
> 		      nvkm_vmm_ptes_get_map()
> 		       func == gp100_vmm_pgt_pfn
> 			struct nvkm_vmm_desc_func gp100_vmm_desc_spt:
> 			  .pfn = gp100_vmm_pgt_pfn
> 			 nvkm_vmm_iter()
> 			  REF_PTES == func == gp100_vmm_pgt_pfn()
> 			    dma_map_page()
> 
> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Tested-by: Ralph Campbell <rcampbell@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   Documentation/vm/hmm.rst                |  26 ++--
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  35 ++----
>   drivers/gpu/drm/nouveau/nouveau_dmem.c  |  27 +---
>   drivers/gpu/drm/nouveau/nouveau_dmem.h  |   3 +-
>   drivers/gpu/drm/nouveau/nouveau_svm.c   |  87 ++++++++-----
>   include/linux/hmm.h                     |  99 ++++++---------
>   mm/hmm.c                                | 160 +++++++++++-------------
>   7 files changed, 192 insertions(+), 245 deletions(-)
> 

...snip...

>   
> +static void nouveau_hmm_convert_pfn(struct nouveau_drm *drm,
> +				    struct hmm_range *range, u64 *ioctl_addr)
> +{
> +	unsigned long i, npages;
> +
> +	/*
> +	 * The ioctl_addr prepared here is passed through nvif_object_ioctl()
> +	 * to an eventual DMA map in something like gp100_vmm_pgt_pfn()
> +	 *
> +	 * This is all just encoding the internal hmm reprensetation into a

s/reprensetation/representation/

Looks good and still tests OK with nouveau.

Re: [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[Jason Gunthorpe]

On Fri, May 01, 2020 at 05:53:26PM -0700, Ralph Campbell wrote:
> > Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> > Tested-by: Ralph Campbell <rcampbell@nvidia.com>
> > Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> >   Documentation/vm/hmm.rst                |  26 ++--
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  35 ++----
> >   drivers/gpu/drm/nouveau/nouveau_dmem.c  |  27 +---
> >   drivers/gpu/drm/nouveau/nouveau_dmem.h  |   3 +-
> >   drivers/gpu/drm/nouveau/nouveau_svm.c   |  87 ++++++++-----
> >   include/linux/hmm.h                     |  99 ++++++---------
> >   mm/hmm.c                                | 160 +++++++++++-------------
> >   7 files changed, 192 insertions(+), 245 deletions(-)
> > 
> 
> ...snip...
> 
> > +static void nouveau_hmm_convert_pfn(struct nouveau_drm *drm,
> > +				    struct hmm_range *range, u64 *ioctl_addr)
> > +{
> > +	unsigned long i, npages;
> > +
> > +	/*
> > +	 * The ioctl_addr prepared here is passed through nvif_object_ioctl()
> > +	 * to an eventual DMA map in something like gp100_vmm_pgt_pfn()
> > +	 *
> > +	 * This is all just encoding the internal hmm reprensetation into a
> 
> s/reprensetation/representation/
> 
> Looks good and still tests OK with nouveau.

Got it, thanks

Jason

Re: [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[John Hubbard]

On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> Presumably the intent here was that hmm_range_fault() could put the data
> into some HW specific format and thus avoid some work. However, nothing
> actually does that, and it isn't clear how anything actually could do that
> as hmm_range_fault() provides CPU addresses which must be DMA mapped.
> 
> Perhaps there is some special HW that does not need DMA mapping, but we
> don't have any examples of this, and the theoretical performance win of
> avoiding an extra scan over the pfns array doesn't seem worth the
> complexity. Plus pfns needs to be scanned anyhow to sort out any
> DEVICE_PRIVATE pages.
> 
> This version replaces the uint64_t with an usigned long containing a pfn
> and fixed flags. On input flags is filled with the HMM_PFN_REQ_* values,
> on successful output it is filled with HMM_PFN_* values, describing the
> state of the pages.
> 

Just some minor stuff below. I wasn't able to spot any errors in the code,
though, so these are just documentation nits.


...

> 
> diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
> index 9924f2caa0184c..c9f2329113a47f 100644
> --- a/Documentation/vm/hmm.rst
> +++ b/Documentation/vm/hmm.rst
> @@ -185,9 +185,6 @@ The usage pattern is::
>         range.start = ...;
>         range.end = ...;
>         range.pfns = ...;

That should be:

           range.hmm_pfns = ...;


> -      range.flags = ...;
> -      range.values = ...;
> -      range.pfn_shift = ...;
>   
>         if (!mmget_not_zero(interval_sub->notifier.mm))
>             return -EFAULT;
> @@ -229,15 +226,10 @@ The hmm_range struct has 2 fields, default_flags and pfn_flags_mask, that specif
>   fault or snapshot policy for the whole range instead of having to set them
>   for each entry in the pfns array.
>   
> -For instance, if the device flags for range.flags are::
> +For instance if the device driver wants pages for a range with at least read
> +permission, it sets::
>   
> -    range.flags[HMM_PFN_VALID] = (1 << 63);
> -    range.flags[HMM_PFN_WRITE] = (1 << 62);
> -
> -and the device driver wants pages for a range with at least read permission,
> -it sets::
> -
> -    range->default_flags = (1 << 63);
> +    range->default_flags = HMM_PFN_REQ_FAULT;
>       range->pfn_flags_mask = 0;
>   
>   and calls hmm_range_fault() as described above. This will fill fault all pages
> @@ -246,18 +238,18 @@ in the range with at least read permission.
>   Now let's say the driver wants to do the same except for one page in the range for
>   which it wants to have write permission. Now driver set::
>   
> -    range->default_flags = (1 << 63);
> -    range->pfn_flags_mask = (1 << 62);
> -    range->pfns[index_of_write] = (1 << 62);
> +    range->default_flags = HMM_PFN_REQ_FAULT;
> +    range->pfn_flags_mask = HMM_PFN_REQ_WRITE;
> +    range->pfns[index_of_write] = HMM_PFN_REQ_WRITE;


All these choices for _WRITE behavior make it slightly confusing. I mean, it's
better than it was, but there are default flags, a mask, and an index as well,
and it looks like maybe we have a little more power and flexibility than
desirable? Nouveau for example is now just setting the mask only:

// nouveau_range_fault():
     .pfn_flags_mask = HMM_PFN_REQ_FAULT | HMM_PFN_REQ_WRITE,
     (.default_flags is not set, so is zero)

Maybe the example should do what Nouveau is doing? And/or do we want to get rid
of either .default_flags or .pfn_flags_mask?

...

> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index cf0d9bd61bebf9..99697df28bfe12 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c

...

> @@ -518,9 +506,45 @@ static const struct mmu_interval_notifier_ops nouveau_svm_mni_ops = {
>   	.invalidate = nouveau_svm_range_invalidate,
>   };
>   
> +static void nouveau_hmm_convert_pfn(struct nouveau_drm *drm,
> +				    struct hmm_range *range, u64 *ioctl_addr)
> +{
> +	unsigned long i, npages;
> +
> +	/*
> +	 * The ioctl_addr prepared here is passed through nvif_object_ioctl()
> +	 * to an eventual DMA map in something like gp100_vmm_pgt_pfn()
> +	 *
> +	 * This is all just encoding the internal hmm reprensetation into a

"representation"

...

> @@ -542,12 +564,15 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
>   			return -EBUSY;
>   
>   		range.notifier_seq = mmu_interval_read_begin(range.notifier);
> -		range.default_flags = 0;
> -		range.pfn_flags_mask = -1UL;
>   		down_read(&mm->mmap_sem);
>   		ret = hmm_range_fault(&range);
>   		up_read(&mm->mmap_sem);
>   		if (ret) {
> +			/*
> +			 * FIXME: the input PFN_REQ flags are destroyed on
> +			 * -EBUSY, we need to regenerate them, also for the
> +			 * other continue below
> +			 */


How serious is this FIXME? It seems like we could get stuck in a loop here,
if we're not issuing a new REQ, right?


>   			if (ret == -EBUSY)
>   				continue;
>   			return ret;
> @@ -562,7 +587,7 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
>   		break;
>   	}
>   
> -	nouveau_dmem_convert_pfn(drm, &range);
> +	nouveau_hmm_convert_pfn(drm, &range, ioctl_addr);
>   
>   	svmm->vmm->vmm.object.client->super = true;
>   	ret = nvif_object_ioctl(&svmm->vmm->vmm.object, data, size, NULL);
> @@ -589,6 +614,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
>   		} i;
>   		u64 phys[16];
>   	} args;
> +	unsigned long hmm_pfns[ARRAY_SIZE(args.phys)];


Is there a risk of blowing up the stack here?

...

> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -19,45 +19,45 @@
>   #include <linux/mmu_notifier.h>
>   
>   /*
> - * hmm_pfn_flag_e - HMM flag enums
> + * On output:
> + * 0             - The page is faultable and a future call with
> + *                 HMM_PFN_REQ_FAULT could succeed.
> + * HMM_PFN_VALID - the pfn field points to a valid PFN. This PFN is at
> + *                 least readable. If dev_private_owner is !NULL then this could
> + *                 point at a DEVICE_PRIVATE page.
> + * HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
> + * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
> + *                 fail. ie poisoned memory, special pages, no vma, etc
>    *
> - * Flags:
> - * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
> - * HMM_PFN_WRITE: CPU page table has write permission set
> - *
> - * The driver provides a flags array for mapping page protections to device
> - * PTE bits. If the driver valid bit for an entry is bit 3,
> - * i.e., (entry & (1 << 3)), then the driver must provide
> - * an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3.
> - * Same logic apply to all flags. This is the same idea as vm_page_prot in vma
> - * except that this is per device driver rather than per architecture.
> + * On input:
> + * 0                 - Return the current state of the page, do not fault it.
> + * HMM_PFN_REQ_FAULT - The output must have HMM_PFN_VALID or hmm_range_fault()
> + *                     will fail
> + * HMM_PFN_REQ_WRITE - The output must have HMM_PFN_WRITE or hmm_range_fault()
> + *                     will fail. Must be combined with HMM_PFN_REQ_FAULT.
>    */
> -enum hmm_pfn_flag_e {
> -	HMM_PFN_VALID = 0,
> -	HMM_PFN_WRITE,
> -	HMM_PFN_FLAG_MAX
> +enum hmm_pfn_flags {

Let's add:

         /* Output flags: */

> +	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
> +	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
> +	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
> +

         /* Input flags: */

...

> @@ -174,44 +162,44 @@ static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
>   	}
>   	if (required_fault)
>   		return hmm_vma_fault(addr, end, required_fault, walk);
> -	return hmm_pfns_fill(addr, end, range, HMM_PFN_NONE);
> +	return hmm_pfns_fill(addr, end, range, 0);
>   }
>   
> -static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
> +static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
> +						 pmd_t pmd)
>   {
>   	if (pmd_protnone(pmd))
>   		return 0;
> -	return pmd_write(pmd) ? range->flags[HMM_PFN_VALID] |
> -				range->flags[HMM_PFN_WRITE] :
> -				range->flags[HMM_PFN_VALID];
> +	return pmd_write(pmd) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;


I always found the previous range->flags[...] approach hard to remember, so it's
nice to see a simpler version now.


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault

[Jason Gunthorpe]

On Mon, May 04, 2020 at 06:30:00PM -0700, John Hubbard wrote:
> On 2020-05-01 11:20, Jason Gunthorpe wrote:
> > From: Jason Gunthorpe <jgg@mellanox.com>
> > 
> > Presumably the intent here was that hmm_range_fault() could put the data
> > into some HW specific format and thus avoid some work. However, nothing
> > actually does that, and it isn't clear how anything actually could do that
> > as hmm_range_fault() provides CPU addresses which must be DMA mapped.
> > 
> > Perhaps there is some special HW that does not need DMA mapping, but we
> > don't have any examples of this, and the theoretical performance win of
> > avoiding an extra scan over the pfns array doesn't seem worth the
> > complexity. Plus pfns needs to be scanned anyhow to sort out any
> > DEVICE_PRIVATE pages.
> > 
> > This version replaces the uint64_t with an usigned long containing a pfn
> > and fixed flags. On input flags is filled with the HMM_PFN_REQ_* values,
> > on successful output it is filled with HMM_PFN_* values, describing the
> > state of the pages.
> > 
> 
> Just some minor stuff below. I wasn't able to spot any errors in the code,
> though, so these are just documentation nits.
> 
> 
> ...
> 
> > 
> > diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
> > index 9924f2caa0184c..c9f2329113a47f 100644
> > +++ b/Documentation/vm/hmm.rst
> > @@ -185,9 +185,6 @@ The usage pattern is::
> >         range.start = ...;
> >         range.end = ...;
> >         range.pfns = ...;
> 
> That should be:
> 
>           range.hmm_pfns = ...;

Yep

> 
> > -      range.flags = ...;
> > -      range.values = ...;
> > -      range.pfn_shift = ...;
> >         if (!mmget_not_zero(interval_sub->notifier.mm))
> >             return -EFAULT;
> > @@ -229,15 +226,10 @@ The hmm_range struct has 2 fields, default_flags and pfn_flags_mask, that specif
> >   fault or snapshot policy for the whole range instead of having to set them
> >   for each entry in the pfns array.
> > -For instance, if the device flags for range.flags are::
> > +For instance if the device driver wants pages for a range with at least read
> > +permission, it sets::
> > -    range.flags[HMM_PFN_VALID] = (1 << 63);
> > -    range.flags[HMM_PFN_WRITE] = (1 << 62);
> > -
> > -and the device driver wants pages for a range with at least read permission,
> > -it sets::
> > -
> > -    range->default_flags = (1 << 63);
> > +    range->default_flags = HMM_PFN_REQ_FAULT;
> >       range->pfn_flags_mask = 0;
> >   and calls hmm_range_fault() as described above. This will fill fault all pages
> > @@ -246,18 +238,18 @@ in the range with at least read permission.
> >   Now let's say the driver wants to do the same except for one page in the range for
> >   which it wants to have write permission. Now driver set::
> > -    range->default_flags = (1 << 63);
> > -    range->pfn_flags_mask = (1 << 62);
> > -    range->pfns[index_of_write] = (1 << 62);
> > +    range->default_flags = HMM_PFN_REQ_FAULT;
> > +    range->pfn_flags_mask = HMM_PFN_REQ_WRITE;
> > +    range->pfns[index_of_write] = HMM_PFN_REQ_WRITE;
> 
> 
> All these choices for _WRITE behavior make it slightly confusing. I mean, it's
> better than it was, but there are default flags, a mask, and an index as well,
> and it looks like maybe we have a little more power and flexibility than
> desirable? Nouveau for example is now just setting the mask only:

The example is showing how to fault all pages but request write for
only certain pages, ie it shows how to use default_flags and pfn_flags
together in probably the only way that could make any sense

> > @@ -542,12 +564,15 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
> >   			return -EBUSY;
> >   		range.notifier_seq = mmu_interval_read_begin(range.notifier);
> > -		range.default_flags = 0;
> > -		range.pfn_flags_mask = -1UL;
> >   		down_read(&mm->mmap_sem);
> >   		ret = hmm_range_fault(&range);
> >   		up_read(&mm->mmap_sem);
> >   		if (ret) {
> > +			/*
> > +			 * FIXME: the input PFN_REQ flags are destroyed on
> > +			 * -EBUSY, we need to regenerate them, also for the
> > +			 * other continue below
> > +			 */
> 
> How serious is this FIXME? It seems like we could get stuck in a loop here,
> if we're not issuing a new REQ, right?

Serious enough someone should fix it and not copy it into other
drivers..
 
> >   			if (ret == -EBUSY)
> >   				continue;
> >   			return ret;
> > @@ -562,7 +587,7 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
> >   		break;
> >   	}
> > -	nouveau_dmem_convert_pfn(drm, &range);
> > +	nouveau_hmm_convert_pfn(drm, &range, ioctl_addr);
> >   	svmm->vmm->vmm.object.client->super = true;
> >   	ret = nvif_object_ioctl(&svmm->vmm->vmm.object, data, size, NULL);
> > @@ -589,6 +614,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
> >   		} i;
> >   		u64 phys[16];
> >   	} args;
> > +	unsigned long hmm_pfns[ARRAY_SIZE(args.phys)];
> 
> 
> Is there a risk of blowing up the stack here?

16*8 is pretty small, but the call stack is very long sadly, since
Ralph succeed it seems OK

> >    */
> > -enum hmm_pfn_flag_e {
> > -	HMM_PFN_VALID = 0,
> > -	HMM_PFN_WRITE,
> > -	HMM_PFN_FLAG_MAX
> > +enum hmm_pfn_flags {
> 
> Let's add:
> 
>         /* Output flags: */
> 
> > +	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
> > +	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
> > +	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
> > +
> 
>         /* Input flags: */

Ok

Thanks,
Jason

Re: [PATCH hmm v2 0/5] Adjust hmm_range_fault() API

[Jason Gunthorpe]

On Fri, May 01, 2020 at 03:20:43PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> The API is a bit complicated for the uses we actually have, and
> disucssions for simplifying have come up a number of times.
> 
> This small series removes the customizable pfn format and simplifies the
> return code of hmm_range_fault()
> 
> All the drivers are adjusted to process in the simplified format.
> I would appreciated tested-by's for the two drivers, thanks!
> 
> v2:
>  - Move call chain to commit message
>  - Fix typo of HMM_PFN_REQ_FAULT
>  - Move nouveau_hmm_convert_pfn() to nouveau_svm.c
>  - Add acks and tested-bys
> v1: https://lore.kernel.org/r/0-v1-4eb72686de3c+5062-hmm_no_flags_jgg@mellanox.com
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> To: Ralph Campbell <rcampbell@nvidia.com>
> Cc: nouveau@lists.freedesktop.org
> Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
> Cc: intel-gfx@lists.freedesktop.org
> Cc: "Kuehling, Felix" <Felix.Kuehling@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
> Cc: amd-gfx@lists.freedesktop.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> Cc: "Yang, Philip" <Philip.Yang@amd.com>
> To: linux-mm@kvack.org
> 
> Jason Gunthorpe (5):
>   mm/hmm: make CONFIG_DEVICE_PRIVATE into a select
>   mm/hmm: make hmm_range_fault return 0 or -1
>   drm/amdgpu: remove dead code after hmm_range_fault()
>   mm/hmm: remove HMM_PFN_SPECIAL
>   mm/hmm: remove the customizable pfn format from hmm_range_fault

Applied to hmm.git, thanks

Jason