On 8/25/2022 11:34 PM, Sean Christopherson wrote:
On Thu, Aug 25, 2022, Xiaoyao Li wrote:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d7f8331d6f7e..3e9ce8f600d2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -38,6 +38,7 @@
#include <asm/fpu/api.h>
#include <asm/fpu/xstate.h>
#include <asm/idtentry.h>
+#include <asm/intel_pt.h>
#include <asm/io.h>
#include <asm/irq_remapping.h>
#include <asm/kexec.h>
@@ -1128,13 +1129,19 @@ static void pt_guest_enter(struct vcpu_vmx *vmx)
if (vmx_pt_mode_is_system())
return;
+ /*
+ * Stop Intel PT on host to avoid vm-entry failure since
+ * VM_ENTRY_LOAD_IA32_RTIT_CTL is set
+ */
+ intel_pt_stop();
+
/*
* GUEST_IA32_RTIT_CTL is already set in the VMCS.
* Save host state before VM entry.
*/
rdmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
KVM's manual save/restore of MSR_IA32_RTIT_CTL should be dropped.
No. It cannot. Please see below.
If PT/RTIT can
trace post-VMXON, then intel_pt_stop() will disable tracing and intel_pt_resume()
will restore the host's desired value.
intel_pt_stop() and intel_pt_resume() touches host's RTIT_CTL only when
host enables/uses Intel PT. Otherwise, they're just noop. In this case,
we cannot assume host's RTIT_CTL is zero (only the RTIT_CTL.TraceEn is
0). After VM-exit, RTIT_CTL is cleared, we need to restore it.
if (vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) {
- wrmsrl(MSR_IA32_RTIT_CTL, 0);
+ /* intel_pt_stop() ensures RTIT_CTL.TraceEn is zero */
pt_save_msr(&vmx->pt_desc.host, vmx->pt_desc.num_address_ranges);
Isn't this at risk of the same corruption? What prevents a PT NMI that arrives
after this point from changing other RTIT MSRs, thus causing KVM to restore the
wrong values?
intel_pt_stop() -> pt_event_stop() will do
WRITE_ONCE(pt->handle_nmi, 0);
which ensure PT NMI handler as noop that at the beginning of
intel_pt_interrupt():
if (!READ_ONCE(pt->handle_nmi))
return;
pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.num_address_ranges);
}
@@ -1156,6 +1163,8 @@ static void pt_guest_exit(struct vcpu_vmx *vmx)
*/
if (vmx->pt_desc.host.ctl)
wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
+
+ intel_pt_resume();
}
void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
--
2.27.0
