Message-ID: <03df0429-9fb2-5326-9bf8-47367818fd49@redhat.com>
Date:   Tue, 21 Mar 2023 09:40:59 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH 0/3] KVM: support the cpu feature FLUSH_L1D
To:     Jim Mattson <jmattson@google.com>
Cc:     kvm@vger.kernel.org, Ben Serebrin <serebrin@google.com>,
        Peter Shier <pshier@google.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Maxim Levitsky <mlevitsk@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
References: <20230201132905.549148-1-eesposit@redhat.com>
 <CALMp9eTt3xzAEoQ038bJQ9LN0ZOXrSWsN7xnNUD+0SS=WwF7Pg@mail.gmail.com>
Content-Language: de-CH
From:   Emanuele Giuseppe Esposito <eesposit@redhat.com>
In-Reply-To: <CALMp9eTt3xzAEoQ038bJQ9LN0ZOXrSWsN7xnNUD+0SS=WwF7Pg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk


Am 20/03/2023 um 17:52 schrieb Jim Mattson:
> On Wed, Feb 1, 2023 at 5:29 AM Emanuele Giuseppe Esposito
> <eesposit@redhat.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