linux-kernel - Re: [PATCH 35/43] KVM: x86: Move setting of sregs during vCPU RESET/INIT to common x86

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Date:   Mon, 17 May 2021 16:50:28 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 35/43] KVM: x86: Move setting of sregs during vCPU
 RESET/INIT to common x86

> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1204,12 +1204,6 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
>         init_sys_seg(&save->ldtr, SEG_TYPE_LDT);
>         init_sys_seg(&save->tr, SEG_TYPE_BUSY_TSS16);
>
> -       svm_set_cr0(vcpu, X86_CR0_NW | X86_CR0_CD | X86_CR0_ET);
> -       svm_set_cr4(vcpu, 0);
> -       svm_set_efer(vcpu, 0);
> -       kvm_set_rflags(vcpu, X86_EFLAGS_FIXED);
> -       vcpu->arch.regs[VCPU_REGS_RIP] = 0x0000fff0;

Reviewed-by: Reiji Watanabe <reijiw@...gle.com>

Those your vCPU RESET/INIT changes look great.

I think the change in init_vmcb() basically assumes that the
function is called from kvm_vcpu_reset(via svm_vcpu_reset()).
Although shutdown_interception() directly calls init_mcb(),
I would think the change doesn't matter for the shutdown
interception case.

IMHO it would be a bit misleading that a function named 'init_vmcb',
which is called from other than kvm_vcpu_reset (svm_vcpu_reset()),
only partially resets the vmcb (probably just to me though).
So, I personally think it would be better if its name or comment
can give some more specific information about the assumption.

BTW, it looks like two lines of "vcpu->arch.hflags = 0;"
can be also removed from the init_vmcb() as well.

Thanks,
Reiji