From: Peter Maydell <peter.maydell@linaro.org>
To: Andrew Jones <drjones@redhat.com>
Cc: Marc Zyngier <maz@kernel.org>,
xu910121@sina.com, Dave Martin <Dave.Martin@arm.com>,
kvmarm <kvmarm@lists.cs.columbia.edu>,
qemu-devel <qemu-devel@nongnu.org>
Subject: Re: Kernel patch cases qemu live migration failed.
Date: Mon, 19 Oct 2020 15:18:11 +0100 [thread overview]
Message-ID: <CAFEAcA8RB6MTnv0qavxWs28=pbT16i9dT1pd+0Dy9HxPVk+bZA@mail.gmail.com> (raw)
In-Reply-To: <20201019134043.vqusmzhqp7owjt6x@kamzik.brq.redhat.com>
On Mon, 19 Oct 2020 at 14:40, Andrew Jones <drjones@redhat.com> wrote:
>
> On Mon, Oct 19, 2020 at 12:43:33PM +0100, Peter Maydell wrote:
> > Well, ID regs are special in the architecture -- they always exist
> > and must RAZ/WI, even if they're not actually given any fields yet.
> > This is different from other "unused" parts of the system register
> > encoding space, which UNDEF.
>
> Table D12-2 confirms the register should be RAZ, as it says the register
> is "RO, but RAZ if SVE is not implemented". Does "RO" imply "WI", though?
> For the guest we inject an exception on writes, and for userspace we
> require the value to be preserved on write.
Sorry, I mis-spoke. They're RAZ, but not WI, just RO (which is to say
they'll UNDEF if you try to write to them).
> I think we should follow the spec, even for userspace access, and be RAZ
> for when the feature isn't implemented. As for writes, assuming the
> exception injection is what we want for the guest (not WI), then that's
> correct. For userspace, I think we should continue forcing preservation
> (which will force preservation of zero when it's RAZ).
Yes, that sounds right.
thanks
-- PMM
next prev parent reply other threads:[~2020-10-19 14:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-15 4:06 Kernel patch cases qemu live migration failed 张东旭
2020-10-15 11:26 ` Marc Zyngier
2020-10-15 13:35 ` Andrew Jones
2020-10-15 13:52 ` Marc Zyngier
2020-10-15 14:41 ` Andrew Jones
2020-10-15 14:57 ` Peter Maydell
2020-10-19 9:25 ` Andrew Jones
2020-10-19 11:32 ` Dave Martin
2020-10-19 11:43 ` Peter Maydell
2020-10-19 13:40 ` Andrew Jones
2020-10-19 14:18 ` Peter Maydell [this message]
2020-10-19 14:58 ` Dave Martin
2020-10-19 15:23 ` Andrew Jones
2020-10-19 16:36 ` Dave Martin
2020-10-15 13:26 ` Andrew Jones
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