[Qemu-devel] [PATCHv4] qemu: enable PV EOI for qemu 1.3

["Michael S. Tsirkin" <mst@redhat.com>]

Enable KVM PV EOI by default. You can still disable it with
-kvm_pv_eoi cpu flag. To avoid breaking cross-version migration,
enable only for qemu 1.3 (or in the future, newer) machine type.

Note:
There don't seem to be any security-related downsides to this patch
because all this does is tell guest about the feature in a convenient
way. A well behaved guest doesn't use a feature unless it's listed but
that's irrelevant for security.

In my testing, with this patch, performance always improved with
no regressions.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

Changes from v3:
    rebased on top of master. document security implications
Changes from v2:
    Address comments by Andreas:
        whitespace fixes and moving function around
Changes from v1:
     Address comments by Eduardo:
         use include instead of duplicate definition
         reduce ifdef spagetti in code using features mask
         rename init from _pv_eoi to _1_3 to enable adding
         more stuff in this version

 hw/pc_piix.c      |  9 ++++++++-
 target-i386/cpu.c | 33 ++++++++++++++++++++-------------
 target-i386/cpu.h |  2 ++
 3 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/hw/pc_piix.c b/hw/pc_piix.c
index bf04a42..1f040cb 100644
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -43,6 +43,7 @@
 #include "xen.h"
 #include "memory.h"
 #include "exec-memory.h"
+#include "cpu.h"
 #ifdef CONFIG_XEN
 #  include <xen/hvm/hvm_info_table.h>
 #endif
@@ -302,6 +303,12 @@ static void pc_init_pci(QEMUMachineInitArgs *args)
              initrd_filename, cpu_model, 1, 1);
 }
 
+static void pc_init_pci_1_3(QEMUMachineInitArgs *args)
+{
+    enable_kvm_pv_eoi();
+    pc_init_pci(args);
+}
+
 static void pc_init_pci_no_kvmclock(QEMUMachineInitArgs *args)
 {
     ram_addr_t ram_size = args->ram_size;
@@ -349,7 +356,7 @@ static QEMUMachine pc_machine_v1_3 = {
     .name = "pc-1.3",
     .alias = "pc",
     .desc = "Standard PC",
-    .init = pc_init_pci,
+    .init = pc_init_pci_1_3,
     .max_cpus = 255,
     .is_default = 1,
 };
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index f3708e6..0f77449 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -124,6 +124,25 @@ typedef struct model_features_t {
 int check_cpuid = 0;
 int enforce_cpuid = 0;
 
+#if defined(CONFIG_KVM)
+static uint32_t kvm_default_features = (1 << KVM_FEATURE_CLOCKSOURCE) |
+        (1 << KVM_FEATURE_NOP_IO_DELAY) |
+        (1 << KVM_FEATURE_MMU_OP) |
+        (1 << KVM_FEATURE_CLOCKSOURCE2) |
+        (1 << KVM_FEATURE_ASYNC_PF) |
+        (1 << KVM_FEATURE_STEAL_TIME) |
+        (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
+static const uint32_t kvm_pv_eoi_features = (0x1 << KVM_FEATURE_PV_EOI);
+#else
+static uint32_t kvm_default_features = 0;
+static const uint32_t kvm_pv_eoi_features = 0;
+#endif
+
+void enable_kvm_pv_eoi(void)
+{
+    kvm_default_features |= kvm_pv_eoi_features;
+}
+
 void host_cpuid(uint32_t function, uint32_t count,
                 uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
 {
@@ -1107,7 +1126,7 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
     /* Features to be added*/
     uint32_t plus_features = 0, plus_ext_features = 0;
     uint32_t plus_ext2_features = 0, plus_ext3_features = 0;
-    uint32_t plus_kvm_features = 0, plus_svm_features = 0;
+    uint32_t plus_kvm_features = kvm_default_features, plus_svm_features = 0;
     uint32_t plus_7_0_ebx_features = 0;
     /* Features to be removed */
     uint32_t minus_features = 0, minus_ext_features = 0;
@@ -1127,18 +1146,6 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
         memcpy(x86_cpu_def, def, sizeof(*def));
     }
 
-#if defined(CONFIG_KVM)
-    plus_kvm_features = (1 << KVM_FEATURE_CLOCKSOURCE) |
-        (1 << KVM_FEATURE_NOP_IO_DELAY) | 
-        (1 << KVM_FEATURE_MMU_OP) |
-        (1 << KVM_FEATURE_CLOCKSOURCE2) |
-        (1 << KVM_FEATURE_ASYNC_PF) | 
-        (1 << KVM_FEATURE_STEAL_TIME) |
-        (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
-#else
-    plus_kvm_features = 0;
-#endif
-
     add_flagname_to_bitmaps("hypervisor", &plus_features,
             &plus_ext_features, &plus_ext2_features, &plus_ext3_features,
             &plus_kvm_features, &plus_svm_features,  &plus_7_0_ebx_features);
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 871c270..de33303 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -1188,4 +1188,6 @@ void do_smm_enter(CPUX86State *env1);
 
 void cpu_report_tpr_access(CPUX86State *env, TPRAccess access);
 
+void enable_kvm_pv_eoi(void);
+
 #endif /* CPU_I386_H */
-- 
MST