[PATCH v2 0/2] arm64: fix the bugs found in the hugetlb test

[PATCH v2 0/2] arm64: fix the bugs found in the hugetlb test

[Huang Shijie]

(1) Backgroud
   For the arm64, the hugetlb page size can be 32M (PMD + Contiguous bit).
   In the 4K page environment, the max page order is 10 (max_order - 1),
   so 32M page is the gigantic page.    

   The arm64 MMU supports a Contiguous bit which is a hint that the PTE
   is one of a set of contiguous entries which can be cached in a single
   TLB entry.  Please refer to the arm64v8 mannul :
       DDI0487A_f_armv8_arm.pdf (in page D4-1811)

(2) The bugs   
   After I tested the libhugetlbfs, I found several bugs in arm64 code.
   This patch set has all the bug fixes for the arm64.
   
(3) The test result in the Softiron and Juno-r1 boards:

   This detail test result shows below (both the "make func" & "make stress"):

    4KB granule:

        1.1) PTE + Contiguous bit : 4K x 16 = 64K (per huge page size)
             Test result          : PASS

        1.2) PMD                  : 2M x  1 = 2M  (per huge page size)
             Test result          : PASS

        1.3) PMD + Contiguous bit : 2M x 16 = 32M (per huge page size)
             Test result          : PASS

    64KB granule:

        3.1) PTE + Contiguous bit : 64K x 32 = 2M (per huge page size)
             Test result          : PASS

        3.2) PMD + Contiguous bit : 512M x 32 = 16G (per huge page size)
             Test result          : no hardware to support this test

v1 -- > v2:
    1.) remove the redundant checks for PGD/PUD


Huang Shijie (2):
  arm64: hugetlb: remove the wrong pmd check in find_num_contig()
  arm64: hugetlb: fix the wrong address for several functions

 arch/arm64/mm/hugetlbpage.c | 20 ++++----------------
 1 file changed, 4 insertions(+), 16 deletions(-)

-- 
2.5.5

[PATCH v2 1/2] arm64: hugetlb: remove the wrong pmd check in find_num_contig()

[Huang Shijie]

The find_num_contig() will return 1 when the pmd is not present.
It will cause a kernel dead loop in the following scenaro:

   1.) pmd entry is not present.

   2.) the page fault occurs:
       ... hugetlb_fault() --> hugetlb_no_page() --> set_huge_pte_at()

   3.) set_huge_pte_at() will only set the first PMD entry, since the
       find_num_contig just return 1 in this case. So the PMD entries
       are all empty except the first one.

   4.) when kernel accesses the address mapped by the second PMD entry,
       a new page fault occurs:
       ... hugetlb_fault() --> huge_ptep_set_access_flags()

       The second PMD entry is still empty now.

   5.) When the kernel returns, the access will cause a page fault again.
       The kernel will run like the "4)" above.
       We will see a dead loop since here.

The dead loop is caught in the 32M hugetlb page (2M PMD + Contiguous bit).

This patch removes wrong pmd check, and fixes this dead loop.

This patch also removes the redundant checks for PGD/PUD in
the find_num_contig().

Acked-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Huang Shijie <shijie.huang@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 2e49bd2..b0d3f8b 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -51,20 +51,8 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
 	*pgsize = PAGE_SIZE;
 	if (!pte_cont(pte))
 		return 1;
-	if (!pgd_present(*pgd)) {
-		VM_BUG_ON(!pgd_present(*pgd));
-		return 1;
-	}
 	pud = pud_offset(pgd, addr);
-	if (!pud_present(*pud)) {
-		VM_BUG_ON(!pud_present(*pud));
-		return 1;
-	}
 	pmd = pmd_offset(pud, addr);
-	if (!pmd_present(*pmd)) {
-		VM_BUG_ON(!pmd_present(*pmd));
-		return 1;
-	}
 	if ((pte_t *)pmd == ptep) {
 		*pgsize = PMD_SIZE;
 		return CONT_PMDS;
-- 
2.5.5

[PATCH v2 2/2] arm64: hugetlb: fix the wrong address for several functions

[Huang Shijie]

The libhugetlbfs meets several failures since the following functions
do not use the correct address:
   huge_ptep_get_and_clear()
   huge_ptep_set_access_flags()
   huge_ptep_set_wrprotect()
   huge_ptep_clear_flush()

This patch fixes the wrong address for them.

Signed-off-by: Huang Shijie <shijie.huang@arm.com>
---
 arch/arm64/mm/hugetlbpage.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index b0d3f8b..fd96ba7 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -200,7 +200,7 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 		ncontig = find_num_contig(mm, addr, cpte, *cpte, &pgsize);
 		/* save the 1st pte to return */
 		pte = ptep_get_and_clear(mm, addr, cpte);
-		for (i = 1; i < ncontig; ++i) {
+		for (i = 1, addr += pgsize; i < ncontig; ++i, addr += pgsize) {
 			/*
 			 * If HW_AFDBM is enabled, then the HW could
 			 * turn on the dirty bit for any of the page
@@ -238,7 +238,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 		pfn = pte_pfn(*cpte);
 		ncontig = find_num_contig(vma->vm_mm, addr, cpte,
 					  *cpte, &pgsize);
-		for (i = 0; i < ncontig; ++i, ++cpte) {
+		for (i = 0; i < ncontig; ++i, ++cpte, addr += pgsize) {
 			changed = ptep_set_access_flags(vma, addr, cpte,
 							pfn_pte(pfn,
 								hugeprot),
@@ -261,7 +261,7 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm,
 
 		cpte = huge_pte_offset(mm, addr);
 		ncontig = find_num_contig(mm, addr, cpte, *cpte, &pgsize);
-		for (i = 0; i < ncontig; ++i, ++cpte)
+		for (i = 0; i < ncontig; ++i, ++cpte, addr += pgsize)
 			ptep_set_wrprotect(mm, addr, cpte);
 	} else {
 		ptep_set_wrprotect(mm, addr, ptep);
@@ -279,7 +279,7 @@ void huge_ptep_clear_flush(struct vm_area_struct *vma,
 		cpte = huge_pte_offset(vma->vm_mm, addr);
 		ncontig = find_num_contig(vma->vm_mm, addr, cpte,
 					  *cpte, &pgsize);
-		for (i = 0; i < ncontig; ++i, ++cpte)
+		for (i = 0; i < ncontig; ++i, ++cpte, addr += pgsize)
 			ptep_clear_flush(vma, addr, cpte);
 	} else {
 		ptep_clear_flush(vma, addr, ptep);
-- 
2.5.5

Re: [PATCH v2 0/2] arm64: fix the bugs found in the hugetlb test

[Catalin Marinas]

On Tue, Nov 08, 2016 at 01:44:37PM +0800, Huang Shijie wrote:
> (3) The test result in the Softiron and Juno-r1 boards:
> 
>    This detail test result shows below (both the "make func" & "make stress"):
> 
>     4KB granule:
> 
>         1.1) PTE + Contiguous bit : 4K x 16 = 64K (per huge page size)
>              Test result          : PASS
> 
>         1.2) PMD                  : 2M x  1 = 2M  (per huge page size)
>              Test result          : PASS
> 
>         1.3) PMD + Contiguous bit : 2M x 16 = 32M (per huge page size)
>              Test result          : PASS
> 
>     64KB granule:
> 
>         3.1) PTE + Contiguous bit : 64K x 32 = 2M (per huge page size)
>              Test result          : PASS
> 
>         3.2) PMD + Contiguous bit : 512M x 32 = 16G (per huge page size)
>              Test result          : no hardware to support this test

Don't we have support for single (non-contiguous) PMD huge page with 64K
pages (512M per huge page)? I gave it a try and it seems to work (though
without your patches applied ;)).

> Huang Shijie (2):
>   arm64: hugetlb: remove the wrong pmd check in find_num_contig()
>   arm64: hugetlb: fix the wrong address for several functions

For these patches:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

I'm not sure whether Will plans to push them into 4.9. AFAICT, the
contiguous huge pages never worked properly, so we may not count it as a
regression but a new feature. If Will doesn't take them, I'll queue the
patches for 4.10.

BTW, I think we also need to fix this (no functional change though):

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 2e49bd252fe7..0a4c97b618ec 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -323,7 +323,7 @@ __setup("hugepagesz=", setup_hugepagesz);
 static __init int add_default_hugepagesz(void)
 {
 	if (size_to_hstate(CONT_PTES * PAGE_SIZE) == NULL)
-		hugetlb_add_hstate(CONT_PMD_SHIFT);
+		hugetlb_add_hstate(CONT_PTE_SHIFT);
 	return 0;
 }
 arch_initcall(add_default_hugepagesz);

-- 
Catalin

Re: [PATCH v2 0/2] arm64: fix the bugs found in the hugetlb test

[Will Deacon]

On Tue, Nov 08, 2016 at 02:09:09PM +0000, Catalin Marinas wrote:
> On Tue, Nov 08, 2016 at 01:44:37PM +0800, Huang Shijie wrote:
> > (3) The test result in the Softiron and Juno-r1 boards:
> > 
> >    This detail test result shows below (both the "make func" & "make stress"):
> > 
> >     4KB granule:
> > 
> >         1.1) PTE + Contiguous bit : 4K x 16 = 64K (per huge page size)
> >              Test result          : PASS
> > 
> >         1.2) PMD                  : 2M x  1 = 2M  (per huge page size)
> >              Test result          : PASS
> > 
> >         1.3) PMD + Contiguous bit : 2M x 16 = 32M (per huge page size)
> >              Test result          : PASS
> > 
> >     64KB granule:
> > 
> >         3.1) PTE + Contiguous bit : 64K x 32 = 2M (per huge page size)
> >              Test result          : PASS
> > 
> >         3.2) PMD + Contiguous bit : 512M x 32 = 16G (per huge page size)
> >              Test result          : no hardware to support this test
> 
> Don't we have support for single (non-contiguous) PMD huge page with 64K
> pages (512M per huge page)? I gave it a try and it seems to work (though
> without your patches applied ;)).
> 
> > Huang Shijie (2):
> >   arm64: hugetlb: remove the wrong pmd check in find_num_contig()
> >   arm64: hugetlb: fix the wrong address for several functions
> 
> For these patches:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> 
> I'm not sure whether Will plans to push them into 4.9. AFAICT, the
> contiguous huge pages never worked properly, so we may not count it as a
> regression but a new feature. If Will doesn't take them, I'll queue the
> patches for 4.10.

Right, given that it's never worked and the failure only seems to crop up
in synthetic testing, I think you can queue these for 4.10.

Will

Re: [PATCH v2 0/2] arm64: fix the bugs found in the hugetlb test

[Huang Shijie]

Hi Will & Catalin,

On Tue, Nov 08, 2016 at 04:36:43PM +0000, Will Deacon wrote:
> On Tue, Nov 08, 2016 at 02:09:09PM +0000, Catalin Marinas wrote:
> > On Tue, Nov 08, 2016 at 01:44:37PM +0800, Huang Shijie wrote:
> > > (3) The test result in the Softiron and Juno-r1 boards:
> > > 
> > >    This detail test result shows below (both the "make func" & "make stress"):
> > > 
> > >     4KB granule:
> > > 
> > >         1.1) PTE + Contiguous bit : 4K x 16 = 64K (per huge page size)
> > >              Test result          : PASS
> > > 
> > >         1.2) PMD                  : 2M x  1 = 2M  (per huge page size)
> > >              Test result          : PASS
> > > 
> > >         1.3) PMD + Contiguous bit : 2M x 16 = 32M (per huge page size)
> > >              Test result          : PASS
> > > 
> > >     64KB granule:
> > > 
> > >         3.1) PTE + Contiguous bit : 64K x 32 = 2M (per huge page size)
> > >              Test result          : PASS
> > > 
> > >         3.2) PMD + Contiguous bit : 512M x 32 = 16G (per huge page size)
> > >              Test result          : no hardware to support this test
> > 
> > Don't we have support for single (non-contiguous) PMD huge page with 64K
> > pages (512M per huge page)? I gave it a try and it seems to work (though
> > without your patches applied ;)).
Yes, it should be okay. This patch set does not affect the the single
PMD huge page.

> > 
> > > Huang Shijie (2):
> > >   arm64: hugetlb: remove the wrong pmd check in find_num_contig()
> > >   arm64: hugetlb: fix the wrong address for several functions
> > 
> > For these patches:
> > 
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Thanks you, Catalin.

> > 
> > I'm not sure whether Will plans to push them into 4.9. AFAICT, the
> > contiguous huge pages never worked properly, so we may not count it as a
> > regression but a new feature. If Will doesn't take them, I'll queue the
> > patches for 4.10.
> 
> Right, given that it's never worked and the failure only seems to crop up
> in synthetic testing, I think you can queue these for 4.10.
Okay. Thank for queue them for 4.10.

Thanks
Huang Shijie