linux-kernel - Re: [PATCH v19 082/130] KVM: TDX: restore user ret MSRs

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Message-ID: <20240412203244.GM3039520@ls.amr.corp.intel.com>
Date: Fri, 12 Apr 2024 13:32:44 -0700
From: Isaku Yamahata <isaku.yamahata@...el.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>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 082/130] KVM: TDX: restore user ret MSRs

On Sun, Apr 07, 2024 at 01:59:03PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:26 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
> 
> Here "Restore" is not accurate, since the previous patch just updates the
> cached value on TD exit.

Sure, let me update it.


> > and before returning to ring 3.  Because TSX_CTRL requires special
> > treat, this patch doesn't address it.
> > 
> > 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 199226c6cf55..7e2b1e554246 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -535,6 +535,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >   	 */
> >   }
> > +struct tdx_uret_msr {
> > +	u32 msr;
> > +	unsigned int slot;
> > +	u64 defval;
> > +};
> > +
> > +static struct tdx_uret_msr tdx_uret_msrs[] = {
> > +	{.msr = MSR_SYSCALL_MASK, .defval = 0x20200 },
> > +	{.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);
> > @@ -627,6 +649,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
> >   	tdx_vcpu_enter_exit(tdx);
> > +	tdx_user_return_update_cache();
> >   	tdx_restore_host_xsave_state(vcpu);
> >   	tdx->host_state_need_restore = true;
> > @@ -1972,6 +1995,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> >   		return -EINVAL;
> >   	}
> > +	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().
> Should be tdx_user_return_update_cache(), if it's the final API name.

Yes, it will be tdx_user_reutrn_msr_update_cache().


> > +		 * Here is setting up cpu feature before running vcpu,
> > +		 * registered is already false.
>                                   ^
>                            remove "already"?

We can this sentence.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>