From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS
Date: Wed, 29 Mar 2017 15:51:44 +0300
Message-ID: <20170329154539-mutt-send-email-mst@kernel.org>
References: <58D17AF0.2010802@arm.com>
 <20170321193933.GB31111@cbox>
 <58DA3F68.6090901@arm.com>
 <20170328112328.GA31156@cbox>
 <20170328115413.GJ23682@e104320-lin>
 <b1c6e747-2fa7-b7a1-60d5-4a9c480b9dc9@huawei.com>
 <58DA67BA.8070404@arm.com>
 <5b7352f4-4965-3ed5-3879-db871797be47@huawei.com>
 <20170329103658.GQ23682@e104320-lin>
 <2a427164-9b37-6711-3a56-906634ba7f12@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Achin Gupta <achin.gupta@arm.com>,
        gengdongjiu <gengdongjiu@huawei.com>, ard.biesheuvel@linaro.org,
        edk2-devel@lists.01.org, qemu-devel@nongnu.org,
        zhaoshenglong@huawei.com, James Morse <james.morse@arm.com>,
        Christoffer Dall <cdall@linaro.org>, xiexiuqi@huawei.com,
        Marc Zyngier <marc.zyngier@arm.com>, catalin.marinas@arm.com,
        will.deacon@arm.com, christoffer.dall@linaro.org,
        rkrcmar@redhat.com, suzuki.poulose@arm.com, andre.przywara@arm.com,
        mark.rutland@arm.com, vladimir.murzin@arm.com,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        wangxiongfeng2@huawei.com, wuquanming@huawei.com,
        huangshaoyu@huawei.com, Leif.Lindholm@linaro.com, nd@arm.com,
        Igor Mammedov <imammedo@redhat.com>
To: Laszlo Ersek <lersek@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <2a427164-9b37-6711-3a56-906634ba7f12@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

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