[v1] x86/boot: Move x86_cache_alignment initialization to correct spot

[PATCH] x86/boot: Move x86_cache_alignment initialization to correct spot

Posted by Dave Hansen 2 years, 2 months ago

c->x86_cache_alignment is initialized from c->x86_clflush_size.
However, commit fbf6449f84bf moved c->x86_clflush_size initialization
to later in boot without moving the c->x86_cache_alignment assignment.

This presumably left c->x86_cache_alignment set to zero for longer
than it should be.

The result was an oops on 32-bit kernels while accessing a pointer
at 0x20.  The 0x20 came from accessing a structure member at offset
0x10 (buffer->cpumask) from a ZERO_SIZE_PTR=0x10.  kmalloc() can
evidently return ZERO_SIZE_PTR when it's given 0 as its alignment
requirement.

Move the c->x86_cache_alignment initialization to be after
c->x86_clflush_size has an actual value.

Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
Cc: Adam Dunlap <acdunlap@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jacob Xu <jacobhxu@google.com>
Link: https://lore.kernel.org/all/20231002200426.GA4127272@dev-arch.thelio-3990X/
---
 arch/x86/kernel/cpu/common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8d7063e4f63c9..9c51ad5bbf319 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1141,6 +1141,7 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
 		}
 	}
 	c->x86_cache_bits = c->x86_phys_bits;
+	c->x86_cache_alignment = c->x86_clflush_size;
 }
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
@@ -1594,8 +1595,6 @@ static void __init cpu_parse_early_param(void)
  */
 static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 {
-	c->x86_cache_alignment = c->x86_clflush_size;
-
 	memset(&c->x86_capability, 0, sizeof(c->x86_capability));
 	c->extended_cpuid_level = 0;
 
-- 
2.34.1

Re: [PATCH] x86/boot: Move x86_cache_alignment initialization to correct spot

Posted by Nathan Chancellor 2 years, 2 months ago

On Mon, Oct 02, 2023 at 03:00:45PM -0700, Dave Hansen wrote:
> c->x86_cache_alignment is initialized from c->x86_clflush_size.
> However, commit fbf6449f84bf moved c->x86_clflush_size initialization
> to later in boot without moving the c->x86_cache_alignment assignment.
> 
> This presumably left c->x86_cache_alignment set to zero for longer
> than it should be.
> 
> The result was an oops on 32-bit kernels while accessing a pointer
> at 0x20.  The 0x20 came from accessing a structure member at offset
> 0x10 (buffer->cpumask) from a ZERO_SIZE_PTR=0x10.  kmalloc() can
> evidently return ZERO_SIZE_PTR when it's given 0 as its alignment
> requirement.
> 
> Move the c->x86_cache_alignment initialization to be after
> c->x86_clflush_size has an actual value.
> 
> Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
> Cc: Adam Dunlap <acdunlap@google.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Jacob Xu <jacobhxu@google.com>
> Link: https://lore.kernel.org/all/20231002200426.GA4127272@dev-arch.thelio-3990X/

Tested-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the quick fix!

> ---
>  arch/x86/kernel/cpu/common.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 8d7063e4f63c9..9c51ad5bbf319 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1141,6 +1141,7 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
>  		}
>  	}
>  	c->x86_cache_bits = c->x86_phys_bits;
> +	c->x86_cache_alignment = c->x86_clflush_size;
>  }
>  
>  static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
> @@ -1594,8 +1595,6 @@ static void __init cpu_parse_early_param(void)
>   */
>  static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>  {
> -	c->x86_cache_alignment = c->x86_clflush_size;
> -
>  	memset(&c->x86_capability, 0, sizeof(c->x86_capability));
>  	c->extended_cpuid_level = 0;
>  
> -- 
> 2.34.1
>

Re: [PATCH] x86/boot: Move x86_cache_alignment initialization to correct spot

Posted by Ingo Molnar 2 years, 2 months ago

* Nathan Chancellor <nathan@kernel.org> wrote:

> On Mon, Oct 02, 2023 at 03:00:45PM -0700, Dave Hansen wrote:
> > c->x86_cache_alignment is initialized from c->x86_clflush_size.
> > However, commit fbf6449f84bf moved c->x86_clflush_size initialization
> > to later in boot without moving the c->x86_cache_alignment assignment.
> > 
> > This presumably left c->x86_cache_alignment set to zero for longer
> > than it should be.
> > 
> > The result was an oops on 32-bit kernels while accessing a pointer
> > at 0x20.  The 0x20 came from accessing a structure member at offset
> > 0x10 (buffer->cpumask) from a ZERO_SIZE_PTR=0x10.  kmalloc() can
> > evidently return ZERO_SIZE_PTR when it's given 0 as its alignment
> > requirement.
> > 
> > Move the c->x86_cache_alignment initialization to be after
> > c->x86_clflush_size has an actual value.
> > 
> > Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
> > Cc: Adam Dunlap <acdunlap@google.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Jacob Xu <jacobhxu@google.com>
> > Link: https://lore.kernel.org/all/20231002200426.GA4127272@dev-arch.thelio-3990X/
> 
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> 
> Thanks for the quick fix!

Thanks for the quick testing - I've applied this fix on top
of fbf6449f84bf in tip:x86/mm.

Dave, I've added your SOB - let me know if that's not OK:

  Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

Thanks,

	Ingo

[tip: x86/mm] x86/boot: Move x86_cache_alignment initialization to correct spot

Posted by tip-bot2 for Dave Hansen 2 years, 2 months ago

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     3e32552652917f10c0aa8ac75cdc8f0b8d257dec
Gitweb:        https://git.kernel.org/tip/3e32552652917f10c0aa8ac75cdc8f0b8d257dec
Author:        Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate:    Mon, 02 Oct 2023 15:00:45 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 03 Oct 2023 09:27:12 +02:00

x86/boot: Move x86_cache_alignment initialization to correct spot

c->x86_cache_alignment is initialized from c->x86_clflush_size.
However, commit fbf6449f84bf moved c->x86_clflush_size initialization
to later in boot without moving the c->x86_cache_alignment assignment:

  fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")

This presumably left c->x86_cache_alignment set to zero for longer
than it should be.

The result was an oops on 32-bit kernels while accessing a pointer
at 0x20.  The 0x20 came from accessing a structure member at offset
0x10 (buffer->cpumask) from a ZERO_SIZE_PTR=0x10.  kmalloc() can
evidently return ZERO_SIZE_PTR when it's given 0 as its alignment
requirement.

Move the c->x86_cache_alignment initialization to be after
c->x86_clflush_size has an actual value.

Fixes: fbf6449f84bf ("x86/sev-es: Set x86_virt_bits to the correct value straight away, instead of a two-phase approach")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20231002220045.1014760-1-dave.hansen@linux.intel.com
---
 arch/x86/kernel/cpu/common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8d7063e..9c51ad5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1141,6 +1141,7 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
 		}
 	}
 	c->x86_cache_bits = c->x86_phys_bits;
+	c->x86_cache_alignment = c->x86_clflush_size;
 }
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
@@ -1594,8 +1595,6 @@ static void __init cpu_parse_early_param(void)
  */
 static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 {
-	c->x86_cache_alignment = c->x86_clflush_size;
-
 	memset(&c->x86_capability, 0, sizeof(c->x86_capability));
 	c->extended_cpuid_level = 0;