Re: [Qemu-devel][PATCH 2/4] Add CET SHSTK and IBT CPUID feature-word definitions.

From: Paolo Bonzini <pbonzini@redhat.com>
To: Yang Weijiang <weijiang.yang@intel.com>,
	qemu-devel@nongnu.org, rkrcmar@redhat.com,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	mst@redhat.com, yu-cheng.yu@intel.com, yi.z.zhang@intel.com,
	hjl.tools@gmail.com
Cc: Zhang Yi <yi.z.zhang@linux.intel.com>
Subject: Re: [Qemu-devel][PATCH 2/4] Add CET SHSTK and IBT CPUID feature-word definitions.
Date: Fri, 28 Dec 2018 15:25:10 +0100	[thread overview]
Message-ID: <97d6366b-df95-cf00-d652-3176547ae5ca@redhat.com> (raw)
In-Reply-To: <30d79c2d6fa0658cd2818c21da852fd4dfeeae1c.1545806972.git.weijiang.yang@intel.com>

On 26/12/18 09:25, Yang Weijiang wrote:
> @@ -1233,6 +1252,14 @@ static const ExtSaveArea x86_ext_save_areas[] = {
>            { .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_PKU,
>              .offset = offsetof(X86XSaveArea, pkru_state),
>              .size = sizeof(XSavePKRU) },
> +    [XSTATE_CET_U_BIT] = {
> +            .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_CET_SHSTK,
> +            .offset = offsetof(X86XSaveArea, cet_u),

These offsets are incorrect, since supervisor states are only stored in
the compacted format.  In fact, in patch 4, supervisor states should
return 0 in CPUID(EAX=0Dh,ECX=n).EBX.

You can use offset == 0 to distinguish supervisor and user states, so
that supervisor states are skipped in xsave_area_size and x86_cpu_reset.

Thanks,

Paolo

> +            .size = sizeof(XSaveCETU) },
> +    [XSTATE_CET_S_BIT] = {
> +            .feature = FEAT_7_0_ECX, .bits = CPUID_7_0_ECX_CET_SHSTK,
> +            .offset = offsetof(X86XSaveArea, cet_s),
> +            .size = sizeof(XSaveCETS) },
>  };
>  
>  static uint32_t xsave_area_size(uint64_t mask)