linux-kernel - Re: [PATCH v19 083/130] KVM: TDX: Add TSX_CTRL msr into uret

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Date: Fri, 12 Apr 2024 13:35:04 -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,
	Yang Weijiang <weijiang.yang@...el.com>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 083/130] KVM: TDX: Add TSX_CTRL msr into uret_msrs
 list

On Sun, Apr 07, 2024 at 03:05:21PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:26 PM, isaku.yamahata@...el.com wrote:
> > From: Yang Weijiang <weijiang.yang@...el.com>
> > 
> > TDX module resets the TSX_CTRL MSR to 0 at TD exit if TSX is enabled for
> > TD. Or it preserves the TSX_CTRL MSR if TSX is disabled for TD.  VMM can
> > rely on uret_msrs mechanism to defer the reload of host value until exiting
> > to user space.
> > 
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> > v19:
> > - fix the type of tdx_uret_tsx_ctrl_slot. unguent int => int.
> > ---
> >   arch/x86/kvm/vmx/tdx.c | 33 +++++++++++++++++++++++++++++++--
> >   arch/x86/kvm/vmx/tdx.h |  8 ++++++++
> >   2 files changed, 39 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 7e2b1e554246..83dcaf5b6fbd 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -547,14 +547,21 @@ static struct tdx_uret_msr tdx_uret_msrs[] = {
> >   	{.msr = MSR_LSTAR,},
> >   	{.msr = MSR_TSC_AUX,},
> >   };
> > +static int tdx_uret_tsx_ctrl_slot;
> > -static void tdx_user_return_update_cache(void)
> > +static void tdx_user_return_update_cache(struct kvm_vcpu *vcpu)
> >   {
> >   	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);
> > +	/*
> > +	 * TSX_CTRL is reset to 0 if guest TSX is supported. Otherwise
> > +	 * preserved.
> > +	 */
> > +	if (to_kvm_tdx(vcpu->kvm)->tsx_supported && tdx_uret_tsx_ctrl_slot != -1)
> 
> If to_kvm_tdx(vcpu->kvm)->tsx_supported is true, tdx_uret_tsx_ctrl_slot
> shouldn't be -1 at this point.
> Otherwise, it's a KVM bug, right?
> Not sure if it needs a warning if tdx_uret_tsx_ctrl_slot is -1, or just
> remove the check?

You're right. Let me remove the != -1 check.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>