linux-kernel - Re: [PATCH v2] KVM: VMX: Fix rflags cache during vCPU reset

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Message-ID: <CANRm+Cx8r5GFwsEHOBv8DVkrcdQHW6CHgD+g5EFXGUTJmysG1Q@mail.gmail.com>
Date:   Tue, 21 Nov 2017 08:34:59 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2] KVM: VMX: Fix rflags cache during vCPU reset

2017-11-21 7:09 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 20/11/2017 23:52, Wanpeng Li wrote:
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index b348920..131fa1c 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -5590,6 +5590,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>               vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
>>       }
>>
>> +     kvm_set_rflags(vcpu, 2);
>>       vmcs_writel(GUEST_RFLAGS, 0x02);
>
> I think the vmcs_writel can go, kvm_set_rflags ends up calling
> vmx_set_rflags.

Agreed.

>
>>       kvm_rip_write(vcpu, 0xfff0);
>>
>>
>
> Beautified testcase:
>
>     #include <unistd.h>
>     #include <sys/syscall.h>
>     #include <string.h>
>     #include <stdint.h>
>     #include <linux/kvm.h>
>     #include <fcntl.h>
>     #include <sys/ioctl.h>
>
>     long r[5];
>     int main()
>     {
>         struct kvm_debugregs dr = { 0 };
>
>         r[2] = open("/dev/kvm", O_RDONLY);
>         r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
>         r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7);
>         struct kvm_guest_debug debug = {
>                 .control = 0xf0403,
>                 .arch = {
>                         .debugreg[6] = 0x2,
>                         .debugreg[7] = 0x2
>                 }
>         };
>         ioctl(r[4], KVM_SET_GUEST_DEBUG, &debug);
>         ioctl(r[4], KVM_RUN, 0);
>     }
>
> No need to do anything, I'll handle this patch after -rc1.

Thanks for that. :)

Regards,
Wanpeng Li