[Xen-devel] [PATCH RFC 36/44] x86/monitor: Capture Xen's intent to use monitor at boot time

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The ACPI idle driver uses an IPI to retrieve cpuid_ecx(5).  This is
problematic because it uses a stack pointer, but also wasteful at runtime.

Introduce X86_FEATURE_XEN_MONITOR as a synthetic feature bit meaning MONITOR
&& EXTENSIONS && INTERRUPT_BREAK, and calculate it when a cpu comes up rather
than repeatedly at runtime.

Drop the duplicate defines for MWAIT cpuid information, and use the
definitions from mwait.h

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/acpi/lib.c           | 16 +---------------
 xen/arch/x86/cpu/common.c         |  7 +++++++
 xen/include/asm-x86/cpufeature.h  |  5 +----
 xen/include/asm-x86/cpufeatures.h |  1 +
 xen/include/asm-x86/mwait.h       |  3 +++
 5 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/xen/arch/x86/acpi/lib.c b/xen/arch/x86/acpi/lib.c
index 7d7c718..1d64e74 100644
--- a/xen/arch/x86/acpi/lib.c
+++ b/xen/arch/x86/acpi/lib.c
@@ -80,16 +80,10 @@ unsigned int acpi_get_processor_id(unsigned int cpu)
        return INVALID_ACPIID;
 }
 
-static void get_mwait_ecx(void *info)
-{
-       *(u32 *)info = cpuid_ecx(CPUID_MWAIT_LEAF);
-}
-
 int arch_acpi_set_pdc_bits(u32 acpi_id, u32 *pdc, u32 mask)
 {
        unsigned int cpu = get_cpu_id(acpi_id);
        struct cpuinfo_x86 *c;
-       u32 ecx;
 
        if (!(acpi_id + 1))
                c = &boot_cpu_data;
@@ -110,15 +104,7 @@ int arch_acpi_set_pdc_bits(u32 acpi_id, u32 *pdc, u32 mask)
         * If mwait/monitor or its break-on-interrupt extension are
         * unsupported, Cx_FFH will be disabled.
         */
-       if (!cpu_has(c, X86_FEATURE_MONITOR) ||
-           c->cpuid_level < CPUID_MWAIT_LEAF)
-               ecx = 0;
-       else if (c == &boot_cpu_data || cpu == smp_processor_id())
-               ecx = cpuid_ecx(CPUID_MWAIT_LEAF);
-       else
-               on_selected_cpus(cpumask_of(cpu), get_mwait_ecx, &ecx, 1);
-       if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
-           !(ecx & CPUID5_ECX_INTERRUPT_BREAK))
+       if ( !cpu_has_xen_monitor )
                pdc[2] &= ~(ACPI_PDC_C_C1_FFH | ACPI_PDC_C_C2C3_FFH);
 
        return 0;
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index decdcd5..262eccc 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -12,6 +12,7 @@
 #include <mach_apic.h>
 #include <asm/setup.h>
 #include <public/sysctl.h> /* for XEN_INVALID_{SOCKET,CORE}_ID */
+#include <asm/mwait.h>
 
 #include "cpu.h"
 
@@ -312,6 +313,12 @@ static void generic_identify(struct cpuinfo_x86 *c)
        if ( cpu_has(c, X86_FEATURE_CLFLUSH) )
                c->x86_clflush_size = ((ebx >> 8) & 0xff) * 8;
 
+       /* Xen only uses MONITOR if INTERRUPT_BREAK is available. */
+       if ( cpu_has(c, X86_FEATURE_MONITOR) &&
+            ((cpuid_ecx(CPUID_MWAIT_LEAF) & CPUID_MWAIT_MIN_FEATURES) ==
+             CPUID_MWAIT_MIN_FEATURES) )
+               set_bit(X86_FEATURE_XEN_MONITOR, c->x86_capability);
+
        if ( (c->cpuid_level >= CPUID_PM_LEAF) &&
             (cpuid_ecx(CPUID_PM_LEAF) & CPUID6_ECX_APERFMPERF_CAPABILITY) )
                set_bit(X86_FEATURE_APERFMPERF, c->x86_capability);
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index 84cc51d..8b24e0e 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -22,10 +22,6 @@
 #define cpu_has(c, bit)                test_bit(bit, (c)->x86_capability)
 #define boot_cpu_has(bit)      test_bit(bit, boot_cpu_data.x86_capability)
 
-#define CPUID_MWAIT_LEAF                5
-#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
-#define CPUID5_ECX_INTERRUPT_BREAK      0x2
-
 #define CPUID_PM_LEAF                    6
 #define CPUID6_ECX_APERFMPERF_CAPABILITY 0x1
 
@@ -104,6 +100,7 @@
 #define cpu_has_arch_perfmon    boot_cpu_has(X86_FEATURE_ARCH_PERFMON)
 #define cpu_has_cpuid_faulting  boot_cpu_has(X86_FEATURE_CPUID_FAULTING)
 #define cpu_has_aperfmperf      boot_cpu_has(X86_FEATURE_APERFMPERF)
+#define cpu_has_xen_monitor     boot_cpu_has(X86_FEATURE_XEN_MONITOR)
 
 enum _cache_type {
     CACHE_TYPE_NULL = 0,
diff --git a/xen/include/asm-x86/cpufeatures.h 
b/xen/include/asm-x86/cpufeatures.h
index bc98227..98637d0 100644
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -22,3 +22,4 @@ XEN_CPUFEATURE(APERFMPERF,      (FSCAPINTS+0)*32+ 8) /* 
APERFMPERF */
 XEN_CPUFEATURE(MFENCE_RDTSC,    (FSCAPINTS+0)*32+ 9) /* MFENCE synchronizes 
RDTSC */
 XEN_CPUFEATURE(XEN_SMEP,        (FSCAPINTS+0)*32+10) /* SMEP gets used by Xen 
itself */
 XEN_CPUFEATURE(XEN_SMAP,        (FSCAPINTS+0)*32+11) /* SMAP gets used by Xen 
itself */
+XEN_CPUFEATURE(XEN_MONITOR,     (FSCAPINTS+0)*32+12) /* Xen uses MONITOR */
diff --git a/xen/include/asm-x86/mwait.h b/xen/include/asm-x86/mwait.h
index ba9c0ea..a1bfeb1 100644
--- a/xen/include/asm-x86/mwait.h
+++ b/xen/include/asm-x86/mwait.h
@@ -9,6 +9,9 @@
 #define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
 #define CPUID5_ECX_INTERRUPT_BREAK     0x2
 
+#define CPUID_MWAIT_MIN_FEATURES \
+    (CPUID5_ECX_EXTENSIONS_SUPPORTED | CPUID5_ECX_INTERRUPT_BREAK)
+
 #define MWAIT_ECX_INTERRUPT_BREAK      0x1
 
 void mwait_idle_with_hints(unsigned int eax, unsigned int ecx);
-- 
2.1.4


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