[v2] TDX support

[RFC PATCH v2 09/44] target/i386: kvm: don't synchronize guest tsc for TD guest

Posted by isaku.yamahata@gmail.com 4 years, 7 months ago

From: Isaku Yamahata <isaku.yamahata@intel.com>

Make kvm_synchronize_all_tsc() nop for TD-guest.

TDX module specification, 9.11.1 TSC Virtualization
"Virtual TSC values are consistent among all the TD;s VCPUs at the
level suppored by the CPU".
There is no need for qemu to synchronize tsc and VMM can't access
to guest TSC. Actually do_kvm_synchronize_tsc() hits assert due to
failure to write to guest tsc.

> qemu/target/i386/kvm.c:235: kvm_get_tsc: Assertion `ret == 1' failed.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 target/i386/kvm/kvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index c29cb420a1..ecb1714920 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -254,7 +254,7 @@ void kvm_synchronize_all_tsc(void)
 {
     CPUState *cpu;
 
-    if (kvm_enabled()) {
+    if (kvm_enabled() && vm_type != KVM_X86_TDX_VM) {
         CPU_FOREACH(cpu) {
             run_on_cpu(cpu, do_kvm_synchronize_tsc, RUN_ON_CPU_NULL);
         }
-- 
2.25.1

Re: [RFC PATCH v2 09/44] target/i386: kvm: don't synchronize guest tsc for TD guest

Posted by Connor Kuehl 4 years, 6 months ago

On 7/7/21 7:54 PM, isaku.yamahata@gmail.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> Make kvm_synchronize_all_tsc() nop for TD-guest.

s/nop/noop

> 
> TDX module specification, 9.11.1 TSC Virtualization

This appears in 9.12.1 of the latest revision as of this writing.

https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-module-1eas-v0.85.039.pdf

> "Virtual TSC values are consistent among all the TD;s VCPUs at the

s/TD;s/TDs

> level suppored by the CPU".

s/suppored/supported

> There is no need for qemu to synchronize tsc and VMM can't access
> to guest TSC. Actually do_kvm_synchronize_tsc() hits assert due to
> failure to write to guest tsc.
> 
>> qemu/target/i386/kvm.c:235: kvm_get_tsc: Assertion `ret == 1' failed.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>

Reviewed-by: Connor Kuehl <ckuehl@redhat.com>