linux-kernel - Re: [PATCH 0/3] KVM: support the cpu feature FLUSH

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Message-ID: <03df0429-9fb2-5326-9bf8-47367818fd49@redhat.com>
Date:   Tue, 21 Mar 2023 09:40:59 +0100
From:   Emanuele Giuseppe Esposito <eesposit@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     kvm@...r.kernel.org, Ben Serebrin <serebrin@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        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>,
        Maxim Levitsky <mlevitsk@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] KVM: support the cpu feature FLUSH_L1D



Am 20/03/2023 um 17:52 schrieb Jim Mattson:
> On Wed, Feb 1, 2023 at 5:29 AM Emanuele Giuseppe Esposito
> <eesposit@...hat.com> wrote:
>>
>> As the title suggest, if the host cpu supports flush_l1d flag and
>> QEMU/userspace wants to boot a VM with the same flag (or emulate same
>> host features), KVM should be able to do so.
>>
>> Patch 3 is the main fix, because if flush_l1d is not advertised by
>> KVM, a linux VM will erroneously mark
>> /sys/devices/system/cpu/vulnerabilities/mmio_stale_data
>> as vulnerable, even though it isn't since the host has the feature
>> and takes care of this. Not sure what would happen in the nested case though.
>>
>> Patch 1 and 2 are just taken and refactored from Jim Mattison's serie that it
>> seems was lost a while ago:
>> https://patchwork.kernel.org/project/kvm/patch/20180814173049.21756-1-jmattson@google.com/
>>
>> I thought it was worth re-posting them.
> 
> What has changed since the patches were originally posted, and Konrad
> dissed them?
> 

>From the upstream conversation, I honestly didn't really catch that
Konrad dissed them. Or at least, I didn't read a valid reason for doing
so, contrary to what Sean instead provided. I thought it was just forgotten.

My bad, next time I will be more careful when trying to resume old
patches :)

Thank you,
Emanuele