[PULL,12/13] target/i386: KVM: allow fast string operations if host supports them

Commit Message

Paolo Bonzini Feb. 27, 2023, 5:55 p.m. UTC

These are just a flag that documents the performance characteristic of
an instruction; it needs no hypervisor support.  So include them even
if KVM does not show them.  In particular, FZRM/FSRS/FSRC have only
been added very recently, but they are available on Sapphire Rapids
processors.

Reviewed-by: Xiaoyao Li <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 target/i386/kvm/kvm.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

Patch

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 587030199192..d18bd2f3e889 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -352,7 +352,7 @@  uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
 {
     struct kvm_cpuid2 *cpuid;
     uint32_t ret = 0;
-    uint32_t cpuid_1_edx;
+    uint32_t cpuid_1_edx, unused;
     uint64_t bitmask;
 
     cpuid = get_supported_cpuid(s);
@@ -399,10 +399,20 @@  uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
     } else if (function == 6 && reg == R_EAX) {
         ret |= CPUID_6_EAX_ARAT; /* safe to allow because of emulated APIC */
     } else if (function == 7 && index == 0 && reg == R_EBX) {
+        /* Not new instructions, just an optimization.  */
+        uint32_t ebx;
+        host_cpuid(7, 0, &unused, &ebx, &unused, &unused);
+        ret |= ebx & CPUID_7_0_EBX_ERMS;
+
         if (host_tsx_broken()) {
             ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE);
         }
     } else if (function == 7 && index == 0 && reg == R_EDX) {
+        /* Not new instructions, just an optimization.  */
+        uint32_t edx;
+        host_cpuid(7, 0, &unused, &unused, &unused, &edx);
+        ret |= edx & CPUID_7_0_EDX_FSRM;
+
         /*
          * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts.
          * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is
@@ -411,6 +421,11 @@  uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         if (!has_msr_arch_capabs) {
             ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES;
         }
+    } else if (function == 7 && index == 1 && reg == R_EAX) {
+        /* Not new instructions, just an optimization.  */
+        uint32_t eax;
+        host_cpuid(7, 1, &eax, &unused, &unused, &unused);
+        ret |= eax & (CPUID_7_1_EAX_FZRM | CPUID_7_1_EAX_FSRS | CPUID_7_1_EAX_FSRC);
     } else if (function == 0xd && index == 0 &&
                (reg == R_EAX || reg == R_EDX)) {
         /*