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Subject: Re: [PATCH] KVM: nvmx: retry writing guest memory after page fault
 injected
From:   Liran Alon <liran.alon@oracle.com>
In-Reply-To: <1577240501-763-1-git-send-email-linmiaohe@huawei.com>
Date:   Thu, 26 Dec 2019 02:20:59 +0200
Cc:     pbonzini@redhat.com, rkrcmar@redhat.com,
        sean.j.christopherson@intel.com, vkuznets@redhat.com,
        wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org
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References: <1577240501-763-1-git-send-email-linmiaohe@huawei.com>
To:     linmiaohe <linmiaohe@huawei.com>
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> On 25 Dec 2019, at 4:21, linmiaohe <linmiaohe@huawei.com> wrote:
>=20
> From: Miaohe Lin <linmiaohe@huawei.com>
>=20
> We should retry writing guest memory when =
kvm_write_guest_virt_system()
> failed and page fault is injected in handle_vmread().
>=20
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Patch fix seems correct to me:
Reviewed-by: Liran Alon <liran.alon@oracle.com>

However, I suggest to rephrase commit title & message as follows:

"""
KVM: nVMX: vmread should not set rflags to specify success in case of =
#PF

In case writing to vmread destination operand result in a #PF, vmread =
should
not call nested_vmx_succeed() to set rflags to specify success. Similar =
to as
done in for VMPTRST (See handle_vmptrst()).
"""

In addition, it will be appreciated if you would also submit =
kvm-unit-test that verifies this condition.

-Liran

> ---
> arch/x86/kvm/vmx/nested.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 8edefdc9c0cb..c1ec9f25a417 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4799,8 +4799,10 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
> 					instr_info, true, len, &gva))
> 			return 1;
> 		/* _system ok, nested_vmx_check_permission has verified =
cpl=3D0 */
> -		if (kvm_write_guest_virt_system(vcpu, gva, &value, len, =
&e))
> +		if (kvm_write_guest_virt_system(vcpu, gva, &value, len, =
&e)) {
> 			kvm_inject_page_fault(vcpu, &e);
> +			return 1;
> +		}
> 	}
>=20
> 	return nested_vmx_succeed(vcpu);
> --=20
> 2.19.1
>=20