[Xen-devel] [PATCH v4 0/2] fix mask calculation in pdx_init_mask

[Xen-devel] [PATCH v4 0/2] fix mask calculation in pdx_init_mask

[Stefano Stabellini]

Hi all,

This is an update on v3 of "fix mask calculation in pdx_init_mask", plus
a cleanup patch.


The following changes since commit 2ac48fd52d846a8c3949373aa0d776c6cb5452db:

  x86/x2APIC: tighten check in cluster mode IPI sending (2019-06-17 17:38:35 +0200)

are available in the Git repository at:

  http://xenbits.xenproject.org/git-http/people/sstabellini/xen-unstable.git 

for you to fetch changes up to cfba65902ec5f15df8b35b3ccf8bcdda695d5665:

  xen/arm: fix mask calculation in pdx_init_mask (2019-06-17 11:46:20 -0700)

----------------------------------------------------------------
Stefano Stabellini (2):
      xen: switch pdx_init_mask to return uint64_t
      xen/arm: fix mask calculation in pdx_init_mask

 xen/arch/arm/setup.c  | 9 ++++++++-
 xen/arch/x86/srat.c   | 2 +-
 xen/common/pdx.c      | 9 +++++++--
 xen/include/xen/pdx.h | 2 +-
 4 files changed, 17 insertions(+), 5 deletions(-)

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

[Xen-devel] [PATCH v4 1/2] xen: switch pdx_init_mask to return uint64_t

[Stefano Stabellini]

Also change srat_region_mask to uint64_t as it is used to store the
return value of pdx_init_mask. uint64_t is always greater or equal to
u64.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
CC: JBeulich@suse.com
CC: andrew.cooper3@citrix.com
CC: julien.grall@arm.com
---
 xen/arch/arm/setup.c  | 2 +-
 xen/arch/x86/srat.c   | 2 +-
 xen/common/pdx.c      | 2 +-
 xen/include/xen/pdx.h | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 2112715579..b03e7ac330 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -483,7 +483,7 @@ static void __init init_pdx(void)
 {
     paddr_t bank_start, bank_size, bank_end;
 
-    u64 mask = pdx_init_mask(bootinfo.mem.bank[0].start);
+    uint64_t mask = pdx_init_mask(bootinfo.mem.bank[0].start);
     int bank;
 
     for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ )
diff --git a/xen/arch/x86/srat.c b/xen/arch/x86/srat.c
index 2d70b45909..47a4267220 100644
--- a/xen/arch/x86/srat.c
+++ b/xen/arch/x86/srat.c
@@ -401,7 +401,7 @@ static int __init nodes_cover_memory(void)
 
 void __init acpi_numa_arch_fixup(void) {}
 
-static u64 __initdata srat_region_mask;
+static uint64_t __initdata srat_region_mask;
 
 static int __init srat_parse_region(struct acpi_subtable_header *header,
 				    const unsigned long end)
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index bb7e437049..8356f03ce8 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -50,7 +50,7 @@ static u64 __init fill_mask(u64 mask)
     return mask;
 }
 
-u64 __init pdx_init_mask(u64 base_addr)
+uint64_t __init pdx_init_mask(uint64_t base_addr)
 {
     return fill_mask(base_addr - 1);
 }
diff --git a/xen/include/xen/pdx.h b/xen/include/xen/pdx.h
index a151aac1a2..770fadc06c 100644
--- a/xen/include/xen/pdx.h
+++ b/xen/include/xen/pdx.h
@@ -13,7 +13,7 @@ extern unsigned long pfn_top_mask, ma_top_mask;
                          (sizeof(*frame_table) & -sizeof(*frame_table)))
 extern unsigned long pdx_group_valid[];
 
-extern u64 pdx_init_mask(u64 base_addr);
+extern uint64_t pdx_init_mask(u64 base_addr);
 extern u64 pdx_region_mask(u64 base, u64 len);
 
 extern void set_pdx_range(unsigned long smfn, unsigned long emfn);
-- 
2.17.1


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

[Xen-devel] [PATCH v4 2/2] xen/arm: fix mask calculation in pdx_init_mask

[Stefano Stabellini]

The mask calculation in pdx_init_mask is wrong when the first bank
starts at address 0x0. The reason is that pdx_init_mask will do '0 - 1'
causing an underflow. As a result, the mask becomes 0xffffffffffffffff
which is the biggest possible mask and ends up causing a significant
memory waste in the frametable size computation.

For instance, on platforms that have a low memory bank starting at 0x0
and a high memory bank, the frametable will end up covering all the
holes in between.

The purpose of the mask is to be passed as a parameter to
pfn_pdx_hole_setup, which based on the mask parameter calculates
pfn_pdx_hole_shift, pfn_pdx_bottom_mask, etc. which are actually the
important masks for frametable initialization later on.

pfn_pdx_hole_setup never compresses addresses below MAX_ORDER bits (1GB
on ARM). Thus, it is safe to initialize mask passing 1ULL << (MAX_ORDER
+ PAGE_SHIFT) as start address to pdx_init_mask.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
CC: JBeulich@suse.com
CC: andrew.cooper3@citrix.com
CC: George.Dunlap@eu.citrix.com
CC: ian.jackson@eu.citrix.com
CC: konrad.wilk@oracle.com
CC: tim@xen.org
CC: wei.liu2@citrix.com
---

Changes in v4:
- use uint64_t
- single line comment code style

Changes in v3:
- improve in-code comments

Unchanged in v3:
- (u64)1

Changes in v2:
- update commit message
- add in-code comments regarding update sites
- improve in-code comments
- move the mask initialization changes to pdx_init_mask
---
 xen/arch/arm/setup.c | 9 ++++++++-
 xen/common/pdx.c     | 7 ++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index b03e7ac330..b0af90e5bf 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -483,7 +483,14 @@ static void __init init_pdx(void)
 {
     paddr_t bank_start, bank_size, bank_end;
 
-    uint64_t mask = pdx_init_mask(bootinfo.mem.bank[0].start);
+    /*
+     * Arm does not have any restrictions on the bits to compress. Pass 0 to
+     * let the common code further restrict the mask.
+     *
+     * If the logic changes in pfn_pdx_hole_setup we might have to
+     * update this function too.
+     */
+    uint64_t mask = pdx_init_mask(0x0);
     int bank;
 
     for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ )
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index 8356f03ce8..9990b94f73 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask)
     return mask;
 }
 
+/* We don't compress the first MAX_ORDER bit of the addresses. */
 uint64_t __init pdx_init_mask(uint64_t base_addr)
 {
-    return fill_mask(base_addr - 1);
+    return fill_mask(max(base_addr,
+                         (uint64_t)1 << (MAX_ORDER + PAGE_SHIFT)) - 1);
 }
 
 u64 __init pdx_region_mask(u64 base, u64 len)
@@ -80,6 +82,9 @@ void __init pfn_pdx_hole_setup(unsigned long mask)
      * This guarantees that page-pointer arithmetic remains valid within
      * contiguous aligned ranges of 2^MAX_ORDER pages. Among others, our
      * buddy allocator relies on this assumption.
+     *
+     * If the logic changes here, we might have to update the ARM specific
+     * init_pdx too.
      */
     for ( j = MAX_ORDER-1; ; )
     {
-- 
2.17.1


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v4 1/2] xen: switch pdx_init_mask to return uint64_t

[Jan Beulich]

>>> On 17.06.19 at 20:50, <sstabellini@kernel.org> wrote:
> Also change srat_region_mask to uint64_t as it is used to store the
> return value of pdx_init_mask. uint64_t is always greater or equal to
> u64.
> 
> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>

Non-Arm bits
Acked-by: Jan Beulich <jbeulich@suse.com>
but could you make the title sound less like it's an actual change
to the function return type? Also it's not just its return type
you change.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v4 1/2] xen: switch pdx_init_mask to return uint64_t

[Julien Grall]

Hi,

On 6/18/19 11:23 AM, Jan Beulich wrote:
>>>> On 17.06.19 at 20:50, <sstabellini@kernel.org> wrote:
>> Also change srat_region_mask to uint64_t as it is used to store the
>> return value of pdx_init_mask. uint64_t is always greater or equal to
>> u64.

I am a bit confused with the last sentence. In which instance, uint64_t 
would be greater to u64? Aren't they meant to both encode a 64-bit value?

>>
>> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
> 
> Non-Arm bits
> Acked-by: Jan Beulich <jbeulich@suse.com>
> but could you make the title sound less like it's an actual change
> to the function return type? Also it's not just its return type
> you change.

To move this series forward, how about the following commit message:

"xen: Replace u64 with uint64_t in pdx_init_mask() and callers

Xen is phasing out the use of u64 in favor of uint64_t.

Therefore, the instance of u64 in the pdx_init_mask() (and the callers) 
are now replaced with uint64_t.

Take the opportunity to also modify srat_region_mask as this is used to 
store the result of pdx_init_mask().
"

Cheers,

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v4 2/2] xen/arm: fix mask calculation in pdx_init_mask

[Julien Grall]

Hi,

On 6/17/19 7:50 PM, Stefano Stabellini wrote:
> The mask calculation in pdx_init_mask is wrong when the first bank
> starts at address 0x0. The reason is that pdx_init_mask will do '0 - 1'
> causing an underflow. As a result, the mask becomes 0xffffffffffffffff
> which is the biggest possible mask and ends up causing a significant
> memory waste in the frametable size computation.
> 
> For instance, on platforms that have a low memory bank starting at 0x0
> and a high memory bank, the frametable will end up covering all the
> holes in between.
> 
> The purpose of the mask is to be passed as a parameter to
> pfn_pdx_hole_setup, which based on the mask parameter calculates
> pfn_pdx_hole_shift, pfn_pdx_bottom_mask, etc. which are actually the
> important masks for frametable initialization later on.
> 
> pfn_pdx_hole_setup never compresses addresses below MAX_ORDER bits (1GB
> on ARM). Thus, it is safe to initialize mask passing 1ULL << (MAX_ORDER
> + PAGE_SHIFT) as start address to pdx_init_mask.
> 
> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>

Reviewed-by: Julien Grall <julien.grall@arm.com>

Ideally, I would like an ack from Andrew or Jan.

> CC: JBeulich@suse.com
> CC: andrew.cooper3@citrix.com
> CC: George.Dunlap@eu.citrix.com
> CC: ian.jackson@eu.citrix.com
> CC: konrad.wilk@oracle.com
> CC: tim@xen.org
> CC: wei.liu2@citrix.com
> ---
> 
> Changes in v4:
> - use uint64_t
> - single line comment code style
> 
> Changes in v3:
> - improve in-code comments
> 
> Unchanged in v3:
> - (u64)1
> 
> Changes in v2:
> - update commit message
> - add in-code comments regarding update sites
> - improve in-code comments
> - move the mask initialization changes to pdx_init_mask
> ---
>   xen/arch/arm/setup.c | 9 ++++++++-
>   xen/common/pdx.c     | 7 ++++++-
>   2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index b03e7ac330..b0af90e5bf 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -483,7 +483,14 @@ static void __init init_pdx(void)
>   {
>       paddr_t bank_start, bank_size, bank_end;
>   
> -    uint64_t mask = pdx_init_mask(bootinfo.mem.bank[0].start);
> +    /*
> +     * Arm does not have any restrictions on the bits to compress. Pass 0 to
> +     * let the common code further restrict the mask.
> +     *
> +     * If the logic changes in pfn_pdx_hole_setup we might have to
> +     * update this function too.
> +     */
> +    uint64_t mask = pdx_init_mask(0x0);
>       int bank;
>   
>       for ( bank = 0 ; bank < bootinfo.mem.nr_banks; bank++ )
> diff --git a/xen/common/pdx.c b/xen/common/pdx.c
> index 8356f03ce8..9990b94f73 100644
> --- a/xen/common/pdx.c
> +++ b/xen/common/pdx.c
> @@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask)
>       return mask;
>   }
>   
> +/* We don't compress the first MAX_ORDER bit of the addresses. */
>   uint64_t __init pdx_init_mask(uint64_t base_addr)
>   {
> -    return fill_mask(base_addr - 1);
> +    return fill_mask(max(base_addr,
> +                         (uint64_t)1 << (MAX_ORDER + PAGE_SHIFT)) - 1);
>   }
>   
>   u64 __init pdx_region_mask(u64 base, u64 len)
> @@ -80,6 +82,9 @@ void __init pfn_pdx_hole_setup(unsigned long mask)
>        * This guarantees that page-pointer arithmetic remains valid within
>        * contiguous aligned ranges of 2^MAX_ORDER pages. Among others, our
>        * buddy allocator relies on this assumption.
> +     *
> +     * If the logic changes here, we might have to update the ARM specific
> +     * init_pdx too.
>        */
>       for ( j = MAX_ORDER-1; ; )
>       {
> 

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v4 1/2] xen: switch pdx_init_mask to return uint64_t

[Jan Beulich]

>>> On 20.06.19 at 15:15, <julien.grall@arm.com> wrote:
> On 6/18/19 11:23 AM, Jan Beulich wrote:
>>>>> On 17.06.19 at 20:50, <sstabellini@kernel.org> wrote:
>>> Also change srat_region_mask to uint64_t as it is used to store the
>>> return value of pdx_init_mask. uint64_t is always greater or equal to
>>> u64.
> 
> I am a bit confused with the last sentence. In which instance, uint64_t 
> would be greater to u64? Aren't they meant to both encode a 64-bit value?

Oh, indeed - somehow I didn't even notice this. If anything it's the other
way around actually, because uint64_t is mandated to be exactly 64 bits
wide, whereas there's no strict specification for u64 afaia, but I very
much assume the intentions there have been the same.

The proposed title and text replacements look fine to me.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v4 2/2] xen/arm: fix mask calculation in pdx_init_mask

[Jan Beulich]

>>> On 20.06.19 at 15:20, <julien.grall@arm.com> wrote:
> On 6/17/19 7:50 PM, Stefano Stabellini wrote:
>> The mask calculation in pdx_init_mask is wrong when the first bank
>> starts at address 0x0. The reason is that pdx_init_mask will do '0 - 1'
>> causing an underflow. As a result, the mask becomes 0xffffffffffffffff
>> which is the biggest possible mask and ends up causing a significant
>> memory waste in the frametable size computation.
>> 
>> For instance, on platforms that have a low memory bank starting at 0x0
>> and a high memory bank, the frametable will end up covering all the
>> holes in between.
>> 
>> The purpose of the mask is to be passed as a parameter to
>> pfn_pdx_hole_setup, which based on the mask parameter calculates
>> pfn_pdx_hole_shift, pfn_pdx_bottom_mask, etc. which are actually the
>> important masks for frametable initialization later on.
>> 
>> pfn_pdx_hole_setup never compresses addresses below MAX_ORDER bits (1GB
>> on ARM). Thus, it is safe to initialize mask passing 1ULL << (MAX_ORDER
>> + PAGE_SHIFT) as start address to pdx_init_mask.
>> 
>> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
> 
> Reviewed-by: Julien Grall <julien.grall@arm.com>
> 
> Ideally, I would like an ack from Andrew or Jan.

Acked-by: Jan Beulich <jbeulich@suse.com>
with one more minor remark:

>> --- a/xen/common/pdx.c
>> +++ b/xen/common/pdx.c
>> @@ -50,9 +50,11 @@ static u64 __init fill_mask(u64 mask)
>>       return mask;
>>   }
>>   
>> +/* We don't compress the first MAX_ORDER bit of the addresses. */
>>   uint64_t __init pdx_init_mask(uint64_t base_addr)

I think the comment would benefit from "want to" getting inserted.
And as a nit, it should be "bits", not "bit", plus perhaps "low" instead
of "first".

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel