Mark the TSC frequency as known when using ACRN's PV CPUID information.
Per commit 81a71f51b89e ("x86/acrn: Set up timekeeping") and common sense,
the TSC freq is explicitly provided by the hypervisor.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/cpu/acrn.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/acrn.c b/arch/x86/kernel/cpu/acrn.c
index dc71a6fdd461..3818f6ae0629 100644
--- a/arch/x86/kernel/cpu/acrn.c
+++ b/arch/x86/kernel/cpu/acrn.c
@@ -40,6 +40,7 @@ static void __init acrn_init_platform(void)
 	if (acrn_tsc_khz_cpuid) {
 		x86_init.hyper.get_tsc_khz = acrn_get_tsc_khz;
 		x86_init.hyper.get_cpu_khz = acrn_get_tsc_khz;
+		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 	}
 }
 
-- 
2.55.0.679.g6767b8d81c-goog

On Thu, 2026-08-06 at 16:35 -0700, Sean Christopherson wrote:
> Mark the TSC frequency as known when using ACRN's PV CPUID information.
> Per commit 81a71f51b89e ("x86/acrn: Set up timekeeping") and common sense,
> the TSC freq is explicitly provided by the hypervisor.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Huh... does this literally get reverted completely in the very *next*
patch in the series? Kind of weird, but I guess in some ways it makes
sense...


Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>

On Sat, Aug 08, 2026, David Woodhouse wrote:
> On Thu, 2026-08-06 at 16:35 -0700, Sean Christopherson wrote:
> > Mark the TSC frequency as known when using ACRN's PV CPUID information.
> > Per commit 81a71f51b89e ("x86/acrn: Set up timekeeping") and common sense,
> > the TSC freq is explicitly provided by the hypervisor.
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> 
> Huh... does this literally get reverted completely in the very *next*
> patch in the series? Kind of weird, but I guess in some ways it makes
> sense...

The literal code gets reverted, but the functional change does not.  Before this
change, ACRN is the only guest-side PV code that doesn't set X86_FEATURE_TSC_KNOWN_FREQ
when the hypervisor provides the exact frequency.  I.e. this patch allows for
making the "No functional change intended" claim in the next patch.