From: Dave Martin <Dave.Martin@arm.com>
To: Andrew Jones <drjones@redhat.com>
Cc: maz@kernel.org, xu910121@sina.com, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2 0/3] KVM: arm64: Fix get-reg-list regression
Date: Tue, 3 Nov 2020 11:37:27 +0000 [thread overview]
Message-ID: <20201103113726.GJ6882@arm.com> (raw)
In-Reply-To: <20201102185037.49248-1-drjones@redhat.com>
On Mon, Nov 02, 2020 at 07:50:34PM +0100, Andrew Jones wrote:
> 张东旭 <xu910121@sina.com> reported a regression seen with CentOS
> when migrating from an old kernel to a new one. The problem was
> that QEMU rejected the migration since KVM_GET_REG_LIST reported
> a register was missing on the destination. Extra registers are OK
> on the destination, but not missing ones. The regression reproduces
> with upstream kernels when migrating from a 4.15 or later kernel,
> up to one with commit 73433762fcae ("KVM: arm64/sve: System register
> context switch and access support"), to a kernel that includes that
> commit, e.g. the latest mainline (5.10-rc2).
>
> The first patch of this series is the fix. The next two patches,
> which don't have any intended functional changes, allow ID_SANITISED
> to be used for registers that flip between exposing features and
> being RAZ, which allows some code to be removed.
Is it worth updating Documentation/virt/kvm/api.rst to clarify the
expected use during VM migrations, and the guarantees that are expected
to hold between migratable kernel versions? Currently the specification
is a mixture of "surely it's obvious" and "whatever makes QEMU work".
I guess that caught me out, but I'll let others judge whether other
people are likely to get similarly confused.
[...]
Cheers
---Dave
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next prev parent reply other threads:[~2020-11-03 11:37 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-02 18:50 [PATCH v2 0/3] KVM: arm64: Fix get-reg-list regression Andrew Jones
2020-11-02 18:50 ` [PATCH v2 1/3] KVM: arm64: Don't hide ID registers from userspace Andrew Jones
2020-11-02 18:50 ` Andrew Jones
2020-11-03 11:18 ` Dave Martin
2020-11-03 11:18 ` Dave Martin
2020-11-03 13:32 ` Andrew Jones
2020-11-03 13:32 ` Andrew Jones
2020-11-04 16:11 ` Dave Martin
2020-11-04 16:11 ` Dave Martin
2020-11-02 18:50 ` [PATCH v2 2/3] KVM: arm64: Check RAZ visibility in ID register accessors Andrew Jones
2020-11-03 11:23 ` Dave Martin
2020-11-03 13:38 ` Andrew Jones
2020-11-04 16:31 ` Dave Martin
2020-11-02 18:50 ` [PATCH v2 3/3] KVM: arm64: Remove AA64ZFR0_EL1 accessors Andrew Jones
2020-11-03 11:32 ` Dave Martin
2020-11-03 13:46 ` Andrew Jones
2020-11-04 16:36 ` Dave Martin
2020-11-03 11:37 ` Dave Martin [this message]
2020-11-03 13:52 ` [PATCH v2 0/3] KVM: arm64: Fix get-reg-list regression Andrew Jones
2020-11-04 16:41 ` Dave Martin
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