Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e7df56e4a00358b6975fae3b70dc9df1282d427a
Commit:     e7df56e4a00358b6975fae3b70dc9df1282d427a
Parent:     94dfbdb3894eda2f673b70e20da2743c4a8d3968
Author:     Avi Kivity <[EMAIL PROTECTED]>
AuthorDate: Wed Mar 14 15:54:54 2007 +0200
Committer:  Avi Kivity <[EMAIL PROTECTED]>
CommitDate: Thu May 3 10:52:32 2007 +0300

    KVM: Remove extraneous guest entry on mmio read
    
    When emulating an mmio read, we actually emulate twice: once to determine
    the physical address of the mmio, and, after we've exited to userspace to
    get the mmio value, we emulate again to place the value in the result
    register and update any flags.
    
    But we don't really need to enter the guest again for that, only to take
    an immediate vmexit.  So, if we detect that we're doing an mmio read,
    emulate a single instruction before entering the guest again.
    
    Signed-off-by: Avi Kivity <[EMAIL PROTECTED]>
---
 drivers/kvm/kvm.h      |    1 +
 drivers/kvm/kvm_main.c |   16 +++++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index f99e89e..41634fd 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -310,6 +310,7 @@ struct kvm_vcpu {
        int mmio_size;
        unsigned char mmio_data[8];
        gpa_t mmio_phys_addr;
+       gva_t mmio_fault_cr2;
        struct kvm_pio_request pio;
        void *pio_data;
 
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index cdf0b17..f267dbb 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1186,6 +1186,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
        int r;
        int cs_db, cs_l;
 
+       vcpu->mmio_fault_cr2 = cr2;
        kvm_arch_ops->cache_regs(vcpu);
 
        kvm_arch_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
@@ -1804,14 +1805,23 @@ static int kvm_vcpu_ioctl_run(struct kvm_vcpu *vcpu, 
struct kvm_run *kvm_run)
                        r = complete_pio(vcpu);
                        if (r)
                                goto out;
-               } else {
+               } else if (!vcpu->mmio_is_write) {
                        memcpy(vcpu->mmio_data, kvm_run->mmio.data, 8);
                        vcpu->mmio_read_completed = 1;
+                       vcpu->mmio_needed = 0;
+                       r = emulate_instruction(vcpu, kvm_run,
+                                           vcpu->mmio_fault_cr2, 0);
+                       if (r == EMULATE_DO_MMIO) {
+                               /*
+                                * Read-modify-write.  Back to userspace.
+                                */
+                               kvm_run->exit_reason = KVM_EXIT_MMIO;
+                               r = 0;
+                               goto out;
+                       }
                }
        }
 
-       vcpu->mmio_needed = 0;
-
        if (kvm_run->exit_reason == KVM_EXIT_HYPERCALL) {
                kvm_arch_ops->cache_regs(vcpu);
                vcpu->regs[VCPU_REGS_RAX] = kvm_run->hypercall.ret;
-
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