KVM: ppc: Stop saving host TLB state

We're saving the host TLB state to memory on every exit, but never using it.
Originally I had thought that we'd want to restore host TLB for heavyweight
exits, but that could actually hurt when context switching to an unrelated host
process (i.e. not qemu).

Since this decreases the performance penalty of all exits, this patch improves
guest boot time by about 15%.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 23bad40..dc3a756 100644 (file)
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -81,8 +81,6 @@ struct kvm_vcpu_arch {
        struct tlbe shadow_tlb[PPC44x_TLB_SIZE];
        /* Pages which are referenced in the shadow TLB. */
        struct page *shadow_pages[PPC44x_TLB_SIZE];
-       /* Copy of the host's TLB. */
-       struct tlbe host_tlb[PPC44x_TLB_SIZE];
 
        u32 host_stack;
        u32 host_pid;

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 92768d3..5940649 100644 (file)
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -356,7 +356,6 @@ int main(void)
 
        DEFINE(VCPU_HOST_STACK, offsetof(struct kvm_vcpu, arch.host_stack));
        DEFINE(VCPU_HOST_PID, offsetof(struct kvm_vcpu, arch.host_pid));
-       DEFINE(VCPU_HOST_TLB, offsetof(struct kvm_vcpu, arch.host_tlb));
        DEFINE(VCPU_SHADOW_TLB, offsetof(struct kvm_vcpu, arch.shadow_tlb));
        DEFINE(VCPU_GPRS, offsetof(struct kvm_vcpu, arch.gpr));
        DEFINE(VCPU_LR, offsetof(struct kvm_vcpu, arch.lr));

diff --git a/arch/powerpc/kvm/booke_interrupts.S b/arch/powerpc/kvm/booke_interrupts.S
index 8eaba26..3e88dfa 100644 (file)
--- a/arch/powerpc/kvm/booke_interrupts.S
+++ b/arch/powerpc/kvm/booke_interrupts.S
@@ -342,26 +342,15 @@ lightweight_exit:
        andc    r6, r5, r6
        mtmsr   r6
 
-       /* Save the host's non-pinned TLB mappings, and load the guest mappings
-        * over them. Leave the host's "pinned" kernel mappings in place. */
-       /* XXX optimization: use generation count to avoid swapping unmodified
-        * entries. */
+       /* Load the guest mappings, leaving the host's "pinned" kernel mappings
+        * in place. */
+       /* XXX optimization: load only modified guest entries. */
        mfspr   r10, SPRN_MMUCR                 /* Save host MMUCR. */
        lis     r8, tlb_44x_hwater@ha
        lwz     r8, tlb_44x_hwater@l(r8)
-       addi    r3, r4, VCPU_HOST_TLB - 4
        addi    r9, r4, VCPU_SHADOW_TLB - 4
        li      r6, 0
 1:
-       /* Save host entry. */
-       tlbre   r7, r6, PPC44x_TLB_PAGEID
-       mfspr   r5, SPRN_MMUCR
-       stwu    r5, 4(r3)
-       stwu    r7, 4(r3)
-       tlbre   r7, r6, PPC44x_TLB_XLAT
-       stwu    r7, 4(r3)
-       tlbre   r7, r6, PPC44x_TLB_ATTRIB
-       stwu    r7, 4(r3)
        /* Load guest entry. */
        lwzu    r7, 4(r9)
        mtspr   SPRN_MMUCR, r7