linux-kernel - Re: [PATCH 0/5] KVM: x86: Handle reserved CR4 bit interception in VMX

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Message-ID: <8bf5e849-3a7d-a30a-061b-0a67a57de865@redhat.com>
Date:   Tue, 20 Oct 2020 11:13:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>
Subject: Re: [PATCH 0/5] KVM: x86: Handle reserved CR4 bit interception in VMX

On 30/09/20 06:16, Sean Christopherson wrote:
> This series stems from Lai's RFC patches to intercept LA57 and let the
> guest own FSGSBASE[*].  Discussion and inspection revealed that KVM does
> not handle the case where LA57 is supported in hardware but not exposed to
> the guest.  This is actually true for all CR4 bits, but LA57 is currently
> the only bit that can be reserved and also owned by the guest.  I have
> a unit test for this that I'll post separately.
> 
> Intercepting LA57 was by far the easiest fix for the immedidate bug, and
> is likely the right change in the long term as there's no justification
> for letting the guest own LA57.
> 
> The middle three patches adjust VMX's CR4 guest/host mask to intercept
> reserved bits.  This required reworking CPUID updates to also refresh said
> mask at the correct time.
> 
> The last past is Lai's, which let's the guest own FSGSBASE.  This depends
> on the reserved bit handling being in place.
> 
> Ran everything through unit tests, and ran the kernel's FSGSBASE selftests
> in a VM.
> 
> [*] https://lkml.kernel.org/r/20200928083047.3349-1-jiangshanlai@gmail.com
> 
> Lai Jiangshan (2):
>   KVM: x86: Intercept LA57 to inject #GP fault when it's reserved
>   KVM: x86: Let the guest own CR4.FSGSBASE
> 
> Sean Christopherson (3):
>   KVM: x86: Invoke vendor's vcpu_after_set_cpuid() after all common
>     updates
>   KVM: x86: Move call to update_exception_bitmap() into VMX code
>   KVM: VMX: Intercept guest reserved CR4 bits to inject #GP fault
> 
>  arch/x86/kvm/cpuid.c          |  6 +++---
>  arch/x86/kvm/kvm_cache_regs.h |  2 +-
>  arch/x86/kvm/vmx/vmx.c        | 18 +++++++++++++-----
>  3 files changed, 17 insertions(+), 9 deletions(-)
> 

Queued, thanks.

Paolo