[PATCH v4 04/47] x86/sev: Don't override CPU frequency calibration for SNP's Secure TSC

[Sean Christopherson <seanjc@xxxxxxxxxx>]

Don't override the kernel's CPU frequency calibration routine when
registering SNP's Secure TSC calibration routine.  SNP (the architecture)
provides zero guarantees that the CPU runs at the same frequency as the
TSC.  The justification for clobbering the CPU routine was:

  Since the difference between CPU base and TSC frequency does not apply
  in this case, the same callback is being used.

but that's simply not true.  E.g. if APERF/MPERF is exposed to the VM, then
the CPU frequency absolutely does matter.

While relying on heuristics and/or the untrusted hypervisor to provide the
CPU frequency isn't ideal, it's at least not outright wrong.

Fixes: 73bbf3b0fbba ("x86/tsc: Init the TSC for Secure TSC guests")
Cc: Nikunj A Dadhania <nikunj@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/coco/sev/core.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index ed0ac52a765e..665de1aea0ee 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2046,7 +2046,6 @@ void __init snp_secure_tsc_init(void)
 
        snp_tsc_freq_khz = SNP_SCALE_TSC_FREQ(tsc_freq_mhz * 1000, 
secrets->tsc_factor);
 
-       x86_platform.calibrate_cpu = securetsc_get_tsc_khz;
        x86_platform.calibrate_tsc = securetsc_get_tsc_khz;
 
        early_memunmap(mem, PAGE_SIZE);
-- 
2.54.0.823.g6e5bcc1fc9-goog