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

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Date:   Tue, 21 Nov 2017 00:09:14 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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

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.

>  	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.

Paolo