linux-kernel - Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

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Date:   Wed, 29 Mar 2017 15:51:44 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Laszlo Ersek <lersek@...hat.com>
Cc:     Achin Gupta <achin.gupta@....com>,
        gengdongjiu <gengdongjiu@...wei.com>, ard.biesheuvel@...aro.org,
        edk2-devel@...ts.01.org, qemu-devel@...gnu.org,
        zhaoshenglong@...wei.com, James Morse <james.morse@....com>,
        Christoffer Dall <cdall@...aro.org>, xiexiuqi@...wei.com,
        Marc Zyngier <marc.zyngier@....com>, catalin.marinas@....com,
        will.deacon@....com, christoffer.dall@...aro.org,
        rkrcmar@...hat.com, suzuki.poulose@....com, andre.przywara@....com,
        mark.rutland@....com, vladimir.murzin@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        wangxiongfeng2@...wei.com, wuquanming@...wei.com,
        huangshaoyu@...wei.com, Leif.Lindholm@...aro.com, nd@....com,
        Igor Mammedov <imammedo@...hat.com>
Subject: Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

On Wed, Mar 29, 2017 at 01:58:29PM +0200, Laszlo Ersek wrote:
> (8) When QEMU gets SIGBUS from the kernel -- I hope that's going to come
> through a signalfd -- QEMU can format the CPER right into guest memory,
> and then inject whatever interrupt (or assert whatever GPIO line) is
> necessary for notifying the guest.

I think I see a race condition potential - what if guest accesses
CPER in guest memory while it's being written?

We can probably use another level of indirection to fix this:

allocate twice the space, add a pointer to where the valid
table is located and update that after writing CPER completely.
The pointer can be written atomically but also needs to
be read atomically, so I suspect it should be a single byte
as we don't know how are OSPMs implementing this.

-- 
MST