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Message-ID: <Zn7gK9KZKxBwgVc_@google.com>
Date: Fri, 28 Jun 2024 09:09:15 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Amit Shah <amit@...nel.org>
Cc: pbonzini@...hat.com, x86@...nel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, amit.shah@....com, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
kim.phillips@....com, david.kaplan@....com
Subject: Re: [PATCH v2] KVM: SVM: let alternatives handle the cases when RSB
filling is required
On Wed, Jun 26, 2024, Amit Shah wrote:
> ---
> arch/x86/kvm/svm/vmenter.S | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
> index a0c8eb37d3e1..2ed80aea3bb1 100644
> --- a/arch/x86/kvm/svm/vmenter.S
> +++ b/arch/x86/kvm/svm/vmenter.S
> @@ -209,10 +209,8 @@ SYM_FUNC_START(__svm_vcpu_run)
> 7: vmload %_ASM_AX
> 8:
>
> -#ifdef CONFIG_MITIGATION_RETPOLINE
> /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
> - FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
> -#endif
> + FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT
Out of an abundance of paranoia, shouldn't this be?
FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT,\
X86_FEATURE_RSB_VMEXIT_LITE
Hmm, but it looks like that would incorrectly trigger the "lite" flavor for
families 0xf - 0x12. I assume those old CPUs aren't affected by whatever on earth
EIBRS_PBRSB is.
/* AMD Family 0xf - 0x12 */
VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_BHI),
VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_BHI),
VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_BHI),
VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_BHI),
/* FAMILY_ANY must be last, otherwise 0x0f - 0x12 matches won't work */
VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_EIBRS_PBRSB | NO_BHI),
VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO | NO_EIBRS_PBRSB | NO_BHI),
>
> /* Clobbers RAX, RCX, RDX. */
> RESTORE_HOST_SPEC_CTRL
> @@ -348,10 +346,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
>
> 2: cli
>
> -#ifdef CONFIG_MITIGATION_RETPOLINE
> /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
> - FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
> -#endif
> + FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT
>
> /* Clobbers RAX, RCX, RDX, consumes RDI (@svm) and RSI (@spec_ctrl_intercepted). */
> RESTORE_HOST_SPEC_CTRL
> --
> 2.45.2
>
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