From: Eduardo Habkost <ehabkost@redhat.com>
To: Bingsong Si <owen.si@ucloud.cn>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Revert "i386: correct cpu_x86_cpuid(0xd)"
Date: Tue, 20 Aug 2019 18:23:06 -0300 [thread overview]
Message-ID: <20190820212306.GM3908@habkost.net> (raw)
In-Reply-To: <20190819100924.14968-1-owen.si@ucloud.cn>
On Mon, Aug 19, 2019 at 06:09:24PM +0800, Bingsong Si wrote:
> This reverts commit de2e68c902f7b6e438b0fa3cfedd74a06a20704f.
>
> Initial value of env->xcr0 == 0, then CPUID(EAX=0xd,ECX=0).EBX == 0, after kvm
> upstream commit 412a3c41, It is ok.
> On host before commit 412a3c41, some legacy guest, i.e. CentOS 6, get
> xstate_size == 0, will crash the guest.
>
> Signed-off-by: Bingsong Si <owen.si@ucloud.cn>
cpu_x86_cpuid() is also used by TCG, and needs to return the
correct data depending on xcr0. If you want to work around a KVM
bug by ignoring xcr0, it needs to be conditional on
kvm_enabled().
But even if we you make this conditional on kvm_enabled(), I
don't understand why QEMU would need a workaround for a KVM bug
that was fixed more than 4 years ago.
> ---
> target/i386/cpu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index ff65e11008..69562e21ed 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -4416,7 +4416,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> *ecx = xsave_area_size(x86_cpu_xsave_components(cpu));
> *eax = env->features[FEAT_XSAVE_COMP_LO];
> *edx = env->features[FEAT_XSAVE_COMP_HI];
> - *ebx = xsave_area_size(env->xcr0);
> + *ebx = *ecx;
> } else if (count == 1) {
> *eax = env->features[FEAT_XSAVE];
> } else if (count < ARRAY_SIZE(x86_ext_save_areas)) {
> --
> 2.22.0
>
>
--
Eduardo
next prev parent reply other threads:[~2019-08-20 21:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 10:09 [Qemu-devel] [PATCH] Revert "i386: correct cpu_x86_cpuid(0xd)" Bingsong Si
2019-08-19 14:34 ` Dr. David Alan Gilbert
2019-08-20 21:23 ` Eduardo Habkost [this message]
2019-08-21 3:04 ` owen.si
2019-08-21 11:19 ` Eduardo Habkost
2019-08-21 11:54 ` owen.si
2019-08-21 20:45 ` Eduardo Habkost
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