linux-kernel - Re: [PATCH v4 0/2] x86: Add the feature Virtual SPEC

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Date:   Wed, 10 Feb 2021 17:40:10 -0600
From:   Babu Moger <babu.moger@....com>
To:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de
Cc:     fenghua.yu@...el.com, tony.luck@...el.com, wanpengli@...cent.com,
        kvm@...r.kernel.org, thomas.lendacky@....com, peterz@...radead.org,
        seanjc@...gle.com, joro@...tes.org, x86@...nel.org,
        kyung.min.park@...el.com, linux-kernel@...r.kernel.org,
        krish.sadhukhan@...cle.com, hpa@...or.com, mgross@...ux.intel.com,
        vkuznets@...hat.com, kim.phillips@....com, wei.huang2@....com,
        jmattson@...gle.com
Subject: Re: [PATCH v4 0/2] x86: Add the feature Virtual SPEC_CTRL

Paolo/Sean,
Any comments on these patches?
Thanks
Babu

On 1/28/21 6:43 PM, Babu Moger wrote:
> Newer AMD processors have a feature to virtualize the use of the
> SPEC_CTRL MSR on the guest. The series adds the feature support
> and enables the feature on SVM.
> ---
> v4:
>   1. Taken care of comments from Sean Christopherson.
>      a. Updated svm_set_msr/svm_get_msr to read/write the spec_ctrl value
>         directly from save spec_ctrl.
>      b. Disabled the msr_interception in init_vmcb when V_SPEC_CTRL is
>         present.
>      c. Added the save restore for nested vm. Also tested to make sure
>         the nested SPEC_CTRL settings properly saved and restored between
>         L2 and L1 guests.
>   2. Added the kvm-unit-tests to verify that. Sent those patches separately.
> 
> v3:
>   1. Taken care of recent changes in vmcb_save_area. Needed to adjust the save
>      area spec_ctrl definition.
>   2. Taken care of few comments from Tom.
>      a. Initialised the save area spec_ctrl in case of SEV-ES.
>      b. Removed the changes in svm_get_msr/svm_set_msr.
>      c. Reverted the changes to disable the msr interception to avoid compatibility
>         issue.
>   3. Updated the patch #1 with Acked-by from Boris.
>   
> v2:
>   NOTE: This is not final yet. Sending out the patches to make
>   sure I captured all the comments correctly.
> 
>   1. Most of the changes are related to Jim and Sean's feedback.
>   2. Improved the description of patch #2.
>   3. Updated the vmcb save area's guest spec_ctrl value(offset 0x2E0)
>      properly. Initialized during init_vmcb and svm_set_msr and
>      returned the value from save area for svm_get_msr.
>   4. As Jim commented, transferred the value into the VMCB prior
>      to VMRUN and out of the VMCB after #VMEXIT.
>   5. Added kvm-unit-test to detect the SPEC CTRL feature.
>      https://lore.kernel.org/kvm/160865324865.19910.5159218511905134908.stgit@bmoger-ubuntu/
>   6. Sean mantioned of renaming MSR_AMD64_VIRT_SPEC_CTRL. But, it might
>      create even more confusion, so dropped the idea for now.
> 
> v3: https://lore.kernel.org/kvm/161073115461.13848.18035972823733547803.stgit@bmoger-ubuntu/
> v2: https://lore.kernel.org/kvm/160867624053.3471.7106539070175910424.stgit@bmoger-ubuntu/
> v1: https://lore.kernel.org/kvm/160738054169.28590.5171339079028237631.stgit@bmoger-ubuntu/
> 
> Babu Moger (2):
>       x86/cpufeatures: Add the Virtual SPEC_CTRL feature
>       KVM: SVM: Add support for Virtual SPEC_CTRL
> 
> 
>  arch/x86/include/asm/cpufeatures.h |    1 +
>  arch/x86/include/asm/svm.h         |    4 +++-
>  arch/x86/kvm/svm/nested.c          |    2 ++
>  arch/x86/kvm/svm/svm.c             |   27 ++++++++++++++++++++++-----
>  4 files changed, 28 insertions(+), 6 deletions(-)
> 
> --
>