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Re: [Qemu-devel] [PATCH] kvm: pass the virtual SEI syndrome to guest OS

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH] kvm: pass the virtual SEI syndrome to guest OS
Date: Wed, 29 Mar 2017 15:51:44 +0300

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.


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