diff mbox series

[v15,08/13] x86/cpu/amd: Do not print FW_BUG for Secure TSC

Message ID 20241203090045.942078-9-nikunj@amd.com (mailing list archive)
State New, archived
Headers show
Series Add Secure TSC support for SNP guests | expand

Commit Message

Nikunj A. Dadhania Dec. 3, 2024, 9 a.m. UTC 
When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
is set, the kernel complains with the below firmware bug:

[Firmware Bug]: TSC doesn't count with P0 frequency!

Secure TSC does not need to run at P0 frequency; the TSC frequency is set
by the VMM as part of the SNP_LAUNCH_START command. Skip this check when
Secure TSC is enabled

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Tested-by: Peter Gonda <pgonda@google.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kernel/cpu/amd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Borislav Petkov Dec. 17, 2024, 11:10 a.m. UTC | #1 
On Tue, Dec 03, 2024 at 02:30:40PM +0530, Nikunj A Dadhania wrote:
> When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
> is set, the kernel complains with the below firmware bug:
> 
> [Firmware Bug]: TSC doesn't count with P0 frequency!

This happens in a normal guest too:

[    0.000000] [Firmware Bug]: TSC doesn't count with P0 frequency!
[    0.000000] BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
...
[    0.000000] DMI: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2023.11-8 02/21/2024
...

If anything, this should check X86_FEATURE_HYPERVISOR but this is just a silly
warning so you don't really need to do anything about it.
Nikunj A. Dadhania Dec. 18, 2024, 5:21 a.m. UTC | #2 
On 12/17/2024 4:40 PM, Borislav Petkov wrote:
> On Tue, Dec 03, 2024 at 02:30:40PM +0530, Nikunj A Dadhania wrote:
>> When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
>> is set, the kernel complains with the below firmware bug:
>>
>> [Firmware Bug]: TSC doesn't count with P0 frequency!
> 
> This happens in a normal guest too:
> 
> [    0.000000] [Firmware Bug]: TSC doesn't count with P0 frequency!
> [    0.000000] BIOS-provided physical RAM map:
> [    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
> ...
> [    0.000000] DMI: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2023.11-8 02/21/2024
> ...
> 
> If anything, this should check X86_FEATURE_HYPERVISOR but this is just a silly
> warning so you don't really need to do anything about it.

In that case, let me drop this patch.

Regards,
Nikunj
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index d8408aafeed9..af9dd545f0ec 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -370,7 +370,8 @@  static void bsp_determine_snp(struct cpuinfo_x86 *c)
 
 static void bsp_init_amd(struct cpuinfo_x86 *c)
 {
-	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
+	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
+	    !cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)) {
 
 		if (c->x86 > 0x10 ||
 		    (c->x86 == 0x10 && c->x86_model >= 0x2)) {