linux-kernel - Re: [PATCH v4 1/1] x86/cpufeatures: Implement Predictive Store Forwarding control.

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Message-ID: <d64b9e19-7124-640f-0ca1-7abc7816d642@amd.com>
Date:   Tue, 4 May 2021 16:01:52 -0500
From:   "Saripalli, RK" <rsaripal@....com>
To:     Reiji Watanabe <reijiw@...gle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, Borislav Petkov <bp@...en8.de>, hpa@...or.com,
        Jonathan Corbet <corbet@....net>, bsd@...hat.com
Subject: Re: [PATCH v4 1/1] x86/cpufeatures: Implement Predictive Store
 Forwarding control.



On 4/30/2021 8:50 PM, Reiji Watanabe wrote:
>>> Considering KVM/virtualization for a CPU that has X86_FEATURE_PSFD
>>> but no other existing feature with MSR_IA32_SPEC_CTRL, if a host
>>> doesn't enable PSFD with the new parameter, the host doesn't have
>>> X86_FEATURE_MSR_SPEC_CTRL.  Then, it would be a problem if its
>>> guests want to use PSFD looking at x86_virt_spec_ctrl().
>>> (I'm not sure how you will change your previous KVM patch though)
>>
>> Reiji, you are correct that X86_FEATURE_MSR_SPEC_CTRL should be enabled so KVM guests can use PSFD
>> even if host does not use it.
>> I have this change in my KVM patch.
> 
> 
> Thank you for the response. Yes, that sounds good.
> 
> Thanks,
> Reiji
> 
Boris / Reiji, I am wondering if I have answered all the questions on these latest patches.
Just checking to see if there are any more changes needed.

Thanks,
RK