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Re: [PATCH linux-next v2] x86/xen/time: prefer tsc as clocksource when it is invariant
- To: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Mon, 12 Dec 2022 13:48:24 -0500
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- Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Anthony Liguori <aliguori@xxxxxxxxxx>, David Reaver <me@xxxxxxxxxxxxxxx>, Brendan Gregg <brendan@xxxxxxxxx>
- Delivery-date: Mon, 12 Dec 2022 18:49:20 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12/12/22 11:05 AM, Krister Johansen wrote:
diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h
index 6daa9b0c8d11..d9d7432481e9 100644
--- a/arch/x86/include/asm/xen/cpuid.h
+++ b/arch/x86/include/asm/xen/cpuid.h
@@ -88,6 +88,12 @@
* EDX: shift amount for tsc->ns conversion
* Sub-leaf 2: EAX: host tsc frequency in kHz
*/
+#define XEN_CPUID_TSC_EMULATED (1u << 0)
+#define XEN_CPUID_HOST_TSC_RELIABLE (1u << 1)
+#define XEN_CPUID_RDTSCP_INSTR_AVAIL (1u << 2)
+#define XEN_CPUID_TSC_MODE_DEFAULT (0)
+#define XEN_CPUID_TSC_MODE_EMULATE (1u)
+#define XEN_CPUID_TSC_MODE_NOEMULATE (2u)
This file is a copy of Xen public interface so this change should go to Xen
first.
+static int __init xen_tsc_safe_clocksource(void)
+{
+ u32 eax, ebx, ecx, edx;
+
+ if (!(xen_hvm_domain() || xen_pvh_domain()))
+ return 0;
+
+ if (!(boot_cpu_has(X86_FEATURE_CONSTANT_TSC)))
+ return 0;
+
+ if (!(boot_cpu_has(X86_FEATURE_NONSTOP_TSC)))
+ return 0;
+
+ if (check_tsc_unstable())
+ return 0;
+
+ cpuid(xen_cpuid_base() + 3, &eax, &ebx, &ecx, &edx);
+
+ if (eax & XEN_CPUID_TSC_EMULATED)
+ return 0;
+
+ if (ebx != XEN_CPUID_TSC_MODE_NOEMULATE)
+ return 0;
Why is the last test needed?
-boris
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