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Date: Thu, 10 Jul 2014 14:47:22 +0200
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Subject: Re: [Qemu-devel] [PATCH v5 00/12] KVM Support for MIPS32 Processors
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To: Peter Maydell <peter.maydell@linaro.org>, James Hogan <james.hogan@imgtec.com>
Cc: kvm-devel <kvm@vger.kernel.org>, Gleb Natapov <gleb@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Sanjay Lal <sanjayl@kymasys.com>, Aurelien Jarno <aurelien@aurel32.net>, Christoffer Dall <christoffer.dall@linaro.org>

Il 10/07/2014 14:17, Peter Maydell ha scritto:
>
> More generally, there doesn't really seem to be provision in the
> KVM KVM_EXIT_MMIO API for returning "this access failed".
> I guess in theory userspace could do all the "figure out how
> to adjust CPU state to do exception entry and then run VCPU",
> but that seems like quite a lot of work which the kernel already
> knows how to do; is there some way to provide a simpler API
> that lets userspace just inform the kernel that it needs to
> fault the access?

There are 3 free padding bytes in struct kvm_run's mmio field.  It's 
possible to add a per-VM capability and have the kernel check one of 
these bytes when the capability is set.

Paolo