linux-kernel - Re: [PATCH v10 072/108] KVM: TDX: restore user ret MSRs

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Message-ID: <20221117201432.GB2751024@ls.amr.corp.intel.com>
Date:   Thu, 17 Nov 2022 12:14:32 -0800
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v10 072/108] KVM: TDX: restore user ret MSRs

On Mon, Nov 14, 2022 at 03:49:32PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> On 10/30/2022 2:23 PM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > Several user ret MSRs are clobbered on TD exit.  Restore those values on
> > TD exit and before returning to ring 3.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> > ---
> >   arch/x86/kvm/vmx/tdx.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 43 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 3ec465cbaeef..f35ccf2b502d 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -456,6 +456,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >   	vcpu->kvm->vm_bugged = true;
> >   }
> > +struct tdx_uret_msr {
> > +	u32 msr;
> > +	unsigned int slot;
> > +	u64 defval;
> > +};
> > +
> > +static struct tdx_uret_msr tdx_uret_msrs[] = {
> > +	{.msr = MSR_SYSCALL_MASK,},
> > +	{.msr = MSR_STAR,},
> > +	{.msr = MSR_LSTAR,},
> > +	{.msr = MSR_TSC_AUX,},
> > +};
> > +
> > +static void tdx_user_return_update_cache(void)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
> > +		kvm_user_return_update_cache(tdx_uret_msrs[i].slot,
> > +					     tdx_uret_msrs[i].defval);
> > +}
> > +
> >   static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
> >   {
> >   	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> > @@ -495,6 +517,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
> >   	tdx_vcpu_enter_exit(vcpu, tdx);
> > +	tdx_user_return_update_cache();
> >   	tdx_restore_host_xsave_state(vcpu);
> >   	tdx->host_state_need_restore = true;
> > @@ -1558,6 +1581,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> >   		return -ENODEV;
> >   	}
> > +	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
> > +		/*
> > +		 * Here it checks if MSRs (tdx_uret_msrs) can be saved/restored
> > +		 * before returning to user space.
> > +		 *
> > +		 * this_cpu_ptr(user_return_msrs)->registered isn't checked
> > +		 * because the registration is done at vcpu runtime by
> > +		 * kvm_set_user_return_msr().
> > +		 * Here is setting up cpu feature before running vcpu,
> > +		 * registered is alreays
> 
> typo, already or always?

already. Thanks.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>