| Message ID | b7a96654fa46593417afa6153959b2989a507842.1708933498.git.isaku.yamahata@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v19,001/130] x86/virt/tdx: Rename _offset to _member for TD_SYSINFO_MAP() macro | expand |
Hi Isaku, On 2/26/2024 12:26 AM, isaku.yamahata@intel.com wrote: > From: Isaku Yamahata <isaku.yamahata@intel.com> > > Because debug store is clobbered, restore it on TD exit. > I am trying to understand why this is needed and finding a few places that seem to indicate that this is not needed. For example, in the TX base spec, section 15.2 "On-TD Performance Monitoring", subsection "15.2.1 Overview": * IA32_DS_AREA MSR is context-switched across TD entry and exit transitions. To confirm I peeked at the TDX module code and found (if I understand this correctly) that IA32_DS_AREA is saved on TD entry (see [1]) and restored on TD exit (see [2]). > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> > --- > arch/x86/events/intel/ds.c | 1 + > arch/x86/kvm/vmx/tdx.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c > index d49d661ec0a7..25670d8a485b 100644 > --- a/arch/x86/events/intel/ds.c > +++ b/arch/x86/events/intel/ds.c > @@ -2428,3 +2428,4 @@ void perf_restore_debug_store(void) > > wrmsrl(MSR_IA32_DS_AREA, (unsigned long)ds); > } > +EXPORT_SYMBOL_GPL(perf_restore_debug_store); > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index b8b168f74dfe..ad4d3d4eaf6c 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -665,6 +665,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) > tdx_vcpu_enter_exit(tdx); > > tdx_user_return_update_cache(vcpu); > + perf_restore_debug_store(); > tdx_restore_host_xsave_state(vcpu); > tdx->host_state_need_restore = true; > Reinette [1] https://github.com/intel/tdx-module/blob/tdx_1.5/src/td_transitions/tdh_vp_enter.c#L719 [2] https://github.com/intel/tdx-module/blob/tdx_1.5/src/td_transitions/td_exit.c#L130
On Tue, Apr 16, 2024 at 11:24:16AM -0700, Reinette Chatre wrote: >Hi Isaku, > >On 2/26/2024 12:26 AM, isaku.yamahata@intel.com wrote: >> From: Isaku Yamahata <isaku.yamahata@intel.com> >> >> Because debug store is clobbered, restore it on TD exit. >> > >I am trying to understand why this is needed and finding a few >places that seem to indicate that this is not needed. > >For example, in the TX base spec, section 15.2 "On-TD Performance >Monitoring", subsection "15.2.1 Overview": > * IA32_DS_AREA MSR is context-switched across TD entry and exit transitions. > >To confirm I peeked at the TDX module code and found (if I understand this >correctly) that IA32_DS_AREA is saved on TD entry (see [1]) and restored on >TD exit (see [2]). Hi Reinette, You are right. I asked TDX module to preserve IA32_DS_AREA across TD transitions and they made this change. So, this patch can be dropped now.
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index d49d661ec0a7..25670d8a485b 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -2428,3 +2428,4 @@ void perf_restore_debug_store(void) wrmsrl(MSR_IA32_DS_AREA, (unsigned long)ds); } +EXPORT_SYMBOL_GPL(perf_restore_debug_store); diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index b8b168f74dfe..ad4d3d4eaf6c 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -665,6 +665,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) tdx_vcpu_enter_exit(tdx); tdx_user_return_update_cache(vcpu); + perf_restore_debug_store(); tdx_restore_host_xsave_state(vcpu); tdx->host_state_need_restore = true;