Re: [XEN PATCH] xen/arm: Hide Pointer Authentication (PAC)

[Julien Grall <julien@xxxxxxx>]

Hi Vladimir,

On 20/01/2021 11:27, Vladimir Murzin wrote:
> The ARMv8.3 Pointer Authentication extension is not supported by Xen
> at the moment, so do not expose that via ID register.
>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> ---
>   xen/arch/arm/cpufeature.c        |  6 +++++
>   xen/include/asm-arm/cpufeature.h | 38 +++++++++++++++++++++++++++++++-
>   2 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
> index 99fe4db28..1d8878380 100644
> --- a/xen/arch/arm/cpufeature.c
> +++ b/xen/arch/arm/cpufeature.c
> @@ -187,6 +187,12 @@ static int __init create_guest_cpuinfo(void)
>   
>       /* Hide MTE support as Xen does not support it */
>       guest_cpuinfo.pfr64.mte = 0;
> +
> +    /* Hide PAC support as Xen does not support it */
> +    guest_cpuinfo.isa64.apa = 0;
> +    guest_cpuinfo.isa64.api = 0;
> +    guest_cpuinfo.isa64.gpa = 0;
> +    guest_cpuinfo.isa64.gpi = 0;
>   #endif
>   
>       /* Hide AMU support */
> diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
> index c6e5711b2..43135abef 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -212,8 +212,44 @@ struct cpuinfo_arm {
>           };
>       } mm64;
>   
> -    struct {
> +    union {
>           uint64_t bits[2];
> +        struct {
> +            /* ISAR0 */
> +            unsigned long __res0:4;
> +            unsigned long aes:4;
> +            unsigned long sha1:4;
> +            unsigned long sha2:4;
> +            unsigned long crc32:4;
> +            unsigned long atomic:4;
> +            unsigned long __res1:4;
> +            unsigned long rdm:4;
> +            unsigned long sha3:4;
> +            unsigned long sm3:4;
> +            unsigned long sm4:4;
> +            unsigned long dp:4;
> +            unsigned long fhm:4;
> +            unsigned long ts:4;
> +            unsigned long tlb:4;
> +            unsigned long rndr:4;
> +
> +            /* ISAR1 */
> +            unsigned long dpb:4;
> +            unsigned long apa:4;
> +            unsigned long api:4;
> +            unsigned long jscvt:4;
> +            unsigned long fcma:4;
> +            unsigned long lrcpc:4;
> +            unsigned long gpa:4;
> +            unsigned long gpi:4;
> +            unsigned long frintts:4;
> +            unsigned long sb:4;
> +            unsigned long specres:4;
> +            unsigned long bf16:4;
> +            unsigned long dgh:4;
> +            unsigned long i8mm:4;
> +            unsigned long __res0:8;
This unfortunately break the build on arm64 becase __res0 is defined 
twiced in the structure:
oss/xen/xen/include/asm/cpufeature.h:251:27: error: duplicate member 
‘__res0’
             unsigned long __res0:8;
                           ^~~~~~

The change is trivial, so I have resolved it (see change below) and 
committed it:
diff --git a/xen/include/asm-arm/cpufeature.h 
b/xen/include/asm-arm/cpufeature.h
index 2baf7919615d..70cb67301f74 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -248,7 +248,7 @@ struct cpuinfo_arm {
             unsigned long bf16:4;
             unsigned long dgh:4;
             unsigned long i8mm:4;
-            unsigned long __res0:8;
+            unsigned long __res2:8;
         };
     } isa64;

Cheers,

--
Julien Grall