linux-kernel - Re: [PATCH v3 1/2] KVM: X86: Processor States following Reset or INIT

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Message-ID: <CANRm+Cyn=BHLrmtmN2eCLah5y4cs7-GxLoDXhQAa1vGrEX=DQw@mail.gmail.com>
Date:   Wed, 11 Oct 2017 08:39:55 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v3 1/2] KVM: X86: Processor States following Reset or INIT

2017-10-11 2:55 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2017-10-09 15:51-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> - XCR0 is reset to 1 by RESET but not INIT
>> - XSS is zeroed by both RESET and INIT
>> - BNDCFGU, BND0-BND3, BNDCFGS are zeroed by both RESET and INIT
>>
>> This patch does this according to SDM.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Jim Mattson <jmattson@...gle.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>> v2 -> v3:
>>  * fix null pointer deference
>>  * fix patch description
>> v1 -> v2:
>>  * XCR0 is not zeroed by INIT
>>  * XSS, BNDCFGU, BND0-BND3, BNDCFGS are zeroed by both RESET and INIT
>>
>>  arch/x86/kvm/vmx.c |  2 ++
>>  arch/x86/kvm/x86.c | 15 +++++++++++++++
>>  2 files changed, 17 insertions(+)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> @@ -7804,18 +7804,33 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>       kvm_async_pf_hash_reset(vcpu);
>>       vcpu->arch.apf.halted = false;
>>
>> +     if (kvm_mpx_supported()) {
>> +             void *mpx_state_buffer;
>> +
>> +             mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu.state.xsave, XFEATURE_MASK_BNDREGS);
>> +             if (mpx_state_buffer)
>> +                     memset(mpx_state_buffer, 0, sizeof(struct mpx_bndreg_state));
>
> I think we should call kvm_put_guest_fpu() before doing this.
> The register might be loaded in CPU and XSAVE instruction from
> vcpu_put() would overwrite any changes we did.

Except in vCPU creation path, vcpu_put() is called in the
destroy/error path, so I think it doesn't matter to overwrite changes
we did.

>
>> +             mpx_state_buffer = get_xsave_addr(&vcpu->arch.guest_fpu.state.xsave, XFEATURE_MASK_BNDCSR);
>> +             if (mpx_state_buffer)
>> +                     memset(mpx_state_buffer, 0, sizeof(u64));
>
> XFEATURE_MASK_BNDCSR is actually
>
>   struct mpx_bndcsr {
>         u64 bndcfgu;
>         u64 bndstatus;
>   } __packed;
>
> So clearing two u64 would be correct, thanks.

SDM section 9.1.1 just mentioned BNDCFGU will be cleared after
RESET/INIT, but not mentioned BNDSTATUS.

Regards,
Wanpeng Li