linux-kernel - Re: [PATCH V3] KVM: arm64: Implement vq

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Message-ID: <20190703174605.GX2790@e103592.cambridge.arm.com>
Date:   Wed, 3 Jul 2019 18:46:08 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     "Zhang, Lei" <zhang.lei@...fujitsu.com>
Cc:     'Viresh Kumar' <viresh.kumar@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry@....com>,
        Suzuki K Pouloze <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "Okamoto, Takayuki" <tokamoto@...fujitsu.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "Mizuma, Masayoshi" <masayoshi.mizuma@...itsu.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Indoh, Takao" <indou.takao@...itsu.com>
Subject: Re: [PATCH V3] KVM: arm64: Implement vq_present() as a macro

On Wed, Jul 03, 2019 at 12:04:11PM +0000, Zhang, Lei wrote:
> Hi guys,
> 
> I can't start up KVM guest os with SVE feature with your patch.
> The error message is 
> qemu-system-aarch64: kvm_init_vcpu failed: Invalid argument.
> 
> My test enviroment.
> kernel  linux-5.2-rc6
> qemu  [Qemu-devel] [PATCH v2 00/14] target/arm/kvm: enable SVE in guests https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
> KVM start up option
> -machine virt,gic-version=host,accel=kvm \
> -cpu host \
> -machine type=virt \
> -nographic \
> -smp 16 \ -m 4096 \
> -drive if=none,file=/root/image.qcow2,id=hd0,format=qcow2 \
> -device virtio-blk-device,drive=hd0 \
> -netdev user,id=mynet0,restrict=off,hostfwd=tcp::38001-:22 \
> -device virtio-net-device,netdev=mynet0 \
> -bios /root/QEMU_EFI.fd
> 
> sve_vq_available function's return value' type is bool.
> But vq_present is macro, so the value is not only TRUE, FALSE but also some numbers.
> So It failed at 
> if (vq_present(vqs, vq) != sve_vq_available(vq)).
> I think it is nessary to make vq_present macro's value only TRUE and FALSE.
> 
> arch/arm64/kvm/guest.c
> static int set_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> 	for (vq = SVE_VQ_MIN; vq <= max_vq; ++vq)
> 		if (vq_present(vqs, vq) != sve_vq_available(vq))　// It failed at here.
> 			return -EINVAL;
> 
> My patch as follows.
> I have started up KVM guest os successfully with SVE feature with this patch.
> 
> Could you review and merge my patch?

[...]

Thanks for reporting this!  It looks like we didn't realise we dropped
the implicit cast to bool when the result was returned from the original
version of vq_present().

Your fix looks sensible to me.

For the future, see Documentation/process/submitting-patches.rst for
guidance on how to prepare a patch for submission.

However, due to the fact that we're already at -rc7 I've written a
commit message for the patch and reposted [1].  Since the fix is yours,
I'll keep your authorship and S-o-B.

Please retest when you can (though the diff should be the same).

Note, your mail seems to be corrupted, but since the diff is a one-line
fix, I'm pretty confident I decoded it correctly.  If anything looks
wrong, please let me know.

[...]

Cheers
---Dave


[1] [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool
http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664745.html