linux-kernel - Re: [PATCH v1 2/6] KVM: x86: Virtualize CR4.LASS

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Message-ID: <ZN1KuB3ZdD/E1tae@google.com>
Date:   Wed, 16 Aug 2023 15:16:24 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Zeng Guang <guang.zeng@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/6] KVM: x86: Virtualize CR4.LASS

Belatedly, same complaints as the LAM series[*], this patch doesn't actually
virtual LASS.  Just squash this with the previous patch, "KVM: VMX: Implement and
apply vmx_is_lass_violation() for LASS protection", though I would keep the
shortlog from this patch.

[*] https://lore.kernel.org/all/ZN1CjTQ0zWiOxk6j@google.com

On Thu, Jun 01, 2023, Zeng Guang wrote:
> Virtualize CR4.LASS[bit 27] under KVM control instead of being guest-owned
> as CR4.LASS generally set once for each vCPU at boot time and won't be
> toggled at runtime. Besides, only if VM has LASS capability enumerated with
> CPUID.(EAX=07H.ECX=1):EAX.LASS[bit 6], KVM allows guest software to be able
> to set CR4.LASS.
> 
> Updating cr4_fixed1 to set CR4.LASS bit in the emulated IA32_VMX_CR4_FIXED1
> MSR for guests and allow guests to enable LASS in nested VMX operaion as well.
> 
> Notes: Setting CR4.LASS to 1 enable LASS in IA-32e mode. It doesn't take
> effect in legacy mode even if CR4.LASS is set.
> 
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> Tested-by: Xuelian Guo <xuelian.guo@...el.com>