[Xen-devel] [PATCH] mask cpuid TSC invariant bit for various circumstances (Take 2)

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Mask cpuid TSC invariant bit for some circumstances
and expose it for others.  On upstream Linux kernels,
non-zero Invariant TSC bit permanently selects TSC
as the clocksource (currently on Intel only).  When
these kernels run on Xen, when migration is possible
and TSC is unemulated, this can cause much weirdness.
But exposing non-zero Invariant TSC has performance
advantages so we want to expose it when it is safe.
(Note leaving it exposed/unexposed for dom0 is not an
issue.)

Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>

diff -r d7d7f978d704 xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c    Tue Oct 20 14:36:01 2009 +0100
+++ b/xen/arch/x86/hvm/hvm.c    Thu Nov 05 11:32:25 2009 -0700
@@ -1796,6 +1796,9 @@ void hvm_cpuid(unsigned int input, unsig
     if ( cpuid_hypervisor_leaves(input, eax, ebx, ecx, edx) )
         return;
 
+    if ( cpuid_time_leaves(input, eax, ebx, ecx, edx) )
+        return;
+
     domain_cpuid(v->domain, input, *ecx, eax, ebx, ecx, edx);
 
     switch ( input )
diff -r d7d7f978d704 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       Tue Oct 20 14:36:01 2009 +0100
+++ b/xen/arch/x86/time.c       Thu Nov 05 11:32:25 2009 -0700
@@ -33,6 +33,7 @@
 #include <asm/hpet.h>
 #include <io_ports.h>
 #include <asm/setup.h> /* for early_time_init */
+#include <public/arch-x86/cpuid.h>
 
 /* opt_clocksource: Force clocksource to one of: pit, hpet, cyclone, acpi. */
 static char __initdata opt_clocksource[10];
@@ -1601,6 +1602,21 @@ void pv_soft_rdtsc(struct vcpu *v, struc
     regs->edx = (uint32_t)(now >> 32);
 }
 
+int cpuid_time_leaves(unsigned int leaf, unsigned int *eax, unsigned int *ebx,
+                                   unsigned int *ecx, unsigned int *edx)
+{
+    struct domain *d = current->domain;
+
+    if ( leaf != XEN_CPUID_APM_FUNCTION )
+        return 0;
+
+    *eax = *ebx = *ecx = 0;
+    *edx = cpuid_edx(leaf);
+    if ( !d->disable_migrate && !d->arch.vtsc )
+        *edx = ~XEN_CPUID_APM_EDX_TSC_INVARIANT;
+    return 1;
+}
+
 /* vtsc may incur measurable performance degradation, diagnose with this */
 static void dump_softtsc(unsigned char key)
 {
diff -r d7d7f978d704 xen/arch/x86/traps.c
--- a/xen/arch/x86/traps.c      Tue Oct 20 14:36:01 2009 +0100
+++ b/xen/arch/x86/traps.c      Thu Nov 05 11:32:25 2009 -0700
@@ -735,7 +735,8 @@ static void pv_cpuid(struct cpu_user_reg
 
     if ( current->domain->domain_id != 0 )
     {
-        if ( !cpuid_hypervisor_leaves(a, &a, &b, &c, &d) )
+        if ( !cpuid_hypervisor_leaves(a, &a, &b, &c, &d) &&
+             !cpuid_time_leaves(a, &a, &b, &c, &d) )
             domain_cpuid(current->domain, a, c, &a, &b, &c, &d);
         goto out;
     }
diff -r d7d7f978d704 xen/include/asm-x86/time.h
--- a/xen/include/asm-x86/time.h        Tue Oct 20 14:36:01 2009 +0100
+++ b/xen/include/asm-x86/time.h        Thu Nov 05 11:32:25 2009 -0700
@@ -45,4 +45,7 @@ void pv_soft_rdtsc(struct vcpu *v, struc
 
 void force_update_vcpu_system_time(struct vcpu *v);
 
+int cpuid_time_leaves(unsigned int leaf, unsigned int *eax, unsigned int *ebx,
+                      unsigned int *ecx, unsigned int *edx);
+
 #endif /* __X86_TIME_H__ */
diff -r d7d7f978d704 xen/include/public/arch-x86/cpuid.h
--- a/xen/include/public/arch-x86/cpuid.h       Tue Oct 20 14:36:01 2009 +0100
+++ b/xen/include/public/arch-x86/cpuid.h       Thu Nov 05 11:32:25 2009 -0700
@@ -65,4 +65,8 @@
 #define _XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD 0
 #define XEN_CPUID_FEAT1_MMU_PT_UPDATE_PRESERVE_AD  (1u<<0)
 
+/* Does the host support TSC Invariance (in Advanced Power Management)? */
+#define XEN_CPUID_APM_FUNCTION          0x80000007
+#define XEN_CPUID_APM_EDX_TSC_INVARIANT (1u<<8)
+
 #endif /* __XEN_PUBLIC_ARCH_X86_CPUID_H__ */

Attachment: cpuid-invariant2.patch
Description: Binary data

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