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 23bad40b0ea6a0262e3592abe64118fa331efe0e..dc3a7562bae4c560870b807d25b6680a22542129 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 92768d3006f7c0800c263bd2d121537fba2a4409..5940649539519365ab4f7dfd0b56fac925b8684e 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 8eaba2613ffd8672d36a7f51d3b1965f48d3d59d..3e88dfa1dbe4ac3fa04046e8825241a2fce0594a 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