kvm_put_one_msr() zeros cpu->kvm_msr_buf and uses it to set one MSR to
KVM. It is pretty wasteful as cpu->kvm_msr_buf is 4096 bytes long;
instead use a local buffer to avoid memset.

Also, expose this method from kvm_i386.h as hyperv.c needs to set MSRs
in a subsequent patch.

Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
---
 target/i386/kvm/kvm.c      | 12 ++++++++----
 target/i386/kvm/kvm_i386.h |  1 +
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index d972eb4705..d19a2913fd 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -2534,12 +2534,16 @@ static void kvm_msr_entry_add(X86CPU *cpu, uint32_t index, uint64_t value)
     msrs->nmsrs++;
 }
 
-static int kvm_put_one_msr(X86CPU *cpu, int index, uint64_t value)
+int kvm_put_one_msr(X86CPU *cpu, int index, uint64_t value)
 {
-    kvm_msr_buf_reset(cpu);
-    kvm_msr_entry_add(cpu, index, value);
+    uint8_t msr_buf[sizeof(struct kvm_msrs) + sizeof(struct kvm_msr_entry)] = { 0 };
+    struct kvm_msrs *msr = (struct kvm_msrs *)msr_buf;
+
+    msr->nmsrs = 1;
+    msr->entries[0].index = index;
+    msr->entries[0].data = value;
 
-    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, cpu->kvm_msr_buf);
+    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, msr);
 }
 
 void kvm_put_apicbase(X86CPU *cpu, uint64_t value)
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index dc72508389..0c4cd08071 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -40,6 +40,7 @@ void kvm_synchronize_all_tsc(void);
 void kvm_arch_reset_vcpu(X86CPU *cs);
 void kvm_arch_do_init_vcpu(X86CPU *cs);
 
+int kvm_put_one_msr(X86CPU *cpu, int index, uint64_t value);
 void kvm_put_apicbase(X86CPU *cpu, uint64_t value);
 
 bool kvm_enable_x2apic(void);
-- 
2.17.1




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879

On 24.05.21 21:54, Siddharth Chandrasekaran wrote:
> kvm_put_one_msr() zeros cpu->kvm_msr_buf and uses it to set one MSR to
> KVM. It is pretty wasteful as cpu->kvm_msr_buf is 4096 bytes long;
> instead use a local buffer to avoid memset.
> 
> Also, expose this method from kvm_i386.h as hyperv.c needs to set MSRs
> in a subsequent patch.
> 
> Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>

Reviewed-by: Alexander Graf <graf@amazon.com>


Alex



Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879