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Re: [PATCH 2/2] i386/cpu: Mask off unsupported XSAVE components
From: |
Eduardo Habkost |
Subject: |
Re: [PATCH 2/2] i386/cpu: Mask off unsupported XSAVE components |
Date: |
Thu, 16 Jul 2020 11:14:31 -0400 |
On Thu, Jul 16, 2020 at 04:20:19PM +0800, Xiaoyao Li wrote:
> When setting up XSAVE components, it needs to mask off those unsupported
> by KVM.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
We must never disable CPUID features silently based on host
capabilities, otherwise we can't guarantee guest ABI stability
when migrating to another host. Filtering of features should
involve a call to mark_unavailable_features() (or some equivalent
mechanism) so we can report the missing features properly through
QMP.
Could you explain what's the bug you are trying to fix? The loop
at x86_cpu_filter_features() is already supposed to disable
features unsupported by the host.
> ---
> target/i386/cpu.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index f5f11603e805..efc92334b7b1 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6274,8 +6274,10 @@ static void x86_cpu_enable_xsave_components(X86CPU
> *cpu)
> }
> }
>
> - env->features[FEAT_XSAVE_COMP_LO] = mask;
> - env->features[FEAT_XSAVE_COMP_HI] = mask >> 32;
> + env->features[FEAT_XSAVE_COMP_LO] = mask &
> + x86_cpu_get_supported_feature_word(FEAT_XSAVE_COMP_LO,
> cpu->migratable);
> + env->features[FEAT_XSAVE_COMP_HI] = (mask >> 32) &
> + x86_cpu_get_supported_feature_word(FEAT_XSAVE_COMP_HI,
> cpu->migratable);
> }
>
> /***** Steps involved on loading and filtering CPUID data
> --
> 2.18.4
>
--
Eduardo