linux-kernel - Re: [PATCH v11 4/6] target-arm: kvm64: detect guest RAS EXTENSION feature

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Date:   Fri, 8 Sep 2017 15:55:53 +0100
From:   Peter Maydell <peter.maydell@...aro.org>
To:     gengdongjiu <gengdongjiu@...wei.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Zhaoshenglong <zhaoshenglong@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        QEMU Developers <qemu-devel@...gnu.org>,
        qemu-arm <qemu-arm@...gnu.org>, kvm-devel <kvm@...r.kernel.org>,
        "edk2-devel@...ts.01.org" <edk2-devel@...ts.01.org>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>,
        James Morse <james.morse@....com>,
        Tyler Baicar <tbaicar@...eaurora.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ingo Molnar <mingo@...nel.org>, "bp@...e.de" <bp@...e.de>,
        Shiju Jose <shiju.jose@...wei.com>,
        "zjzhang@...eaurora.org" <zjzhang@...eaurora.org>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        John Garry <john.garry@...wei.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        huangdaode <huangdaode@...ilicon.com>,
        "Wangzhou (B)" <wangzhou1@...ilicon.com>,
        Huangshaoyu <huangshaoyu@...wei.com>,
        Wuquanming <wuquanming@...wei.com>,
        Linuxarm <linuxarm@...wei.com>,
        "Zhengqiang (turing)" <zhengqiang10@...wei.com>
Subject: Re: [PATCH v11 4/6] target-arm: kvm64: detect guest RAS EXTENSION feature

On 8 September 2017 at 15:26, gengdongjiu <gengdongjiu@...wei.com> wrote:


>> Shouldn't we need to also tell the kernel that we actually want
>> it to expose RAS to the guest? Compare the PMU code in this function,
>> where we set a kvm_init_features bit to do this.

> In the PMU code, it indeed sets a kvm_init_features bit. Here ARM
> James has a concern that we are depend on the host CPU RAS extension,
> He means that if userspace receives the SIGBUS delivered by host
> memory_failure(), user space should record the CPER for guest
> and handling the error regardless whether host CPU supports RAS
> extension. But I think if user space receives the SIGBUS signal,
> that means
> host CPU RAS module detects the error or CPU consumes the poison
> data, thus we should check whether physical CPU support RAS extension.

I don't understand what you have in mind here. If the host does
not support the CPU RAS extension then we should never get a
SIGBUS in the first place.

In any case this doesn't seem relevant to the question of whether it
should be optional to expose the RAS extension to the *guest*.
Even if the host does support RAS, you should be able to run a
VM that knows nothing about RAS.

thanks
-- PMM