KVM: ppc: directly insert shadow mappings into the hardware TLB

Formerly, we used to maintain a per-vcpu shadow TLB and on every entry to the
guest would load this array into the hardware TLB. This consumed 1280 bytes of
memory (64 entries of 16 bytes plus a struct page pointer each), and also
required some assembly to loop over the array on every entry.

Instead of saving a copy in memory, we can just store shadow mappings directly
into the hardware TLB, accepting that the host kernel will clobber these as
part of the normal 440 TLB round robin. When we do that we need less than half
the memory, and we have decreased the exit handling time for all guest exits,
at the cost of increased number of TLB misses because the host overwrites some
guest entries.

These savings will be increased on processors with larger TLBs or which
implement intelligent flush instructions like tlbivax (which will avoid the
need to walk arrays in software).

In addition to that and to the code simplification, we have a greater chance of
leaving other host userspace mappings in the TLB, instead of forcing all
subsequent tasks to re-fault all their mappings.

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

1 files changed, 16 insertions, 10 deletions

diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 924c7b4b1107..eb24383c87d2 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -24,10 +24,12 @@
 #include <linux/module.h>
 #include <linux/vmalloc.h>
 #include <linux/fs.h>
+
 #include <asm/cputable.h>
 #include <asm/uaccess.h>
 #include <asm/kvm_ppc.h>
 #include <asm/cacheflush.h>
+#include <asm/kvm_44x.h>
 
 #include "booke.h"
 #include "44x_tlb.h"
@@ -207,10 +209,6 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                  * handled this interrupt the moment we enabled interrupts.
                  * Now we just offer it a chance to reschedule the guest. */
 
-                /* XXX At this point the TLB still holds our shadow TLB, so if
-                 * we do reschedule the host will fault over it. Perhaps we
-                 * should politely restore the host's entries to minimize
-                 * misses before ceding control. */
                 vcpu->stat.dec_exits++;
                 if (need_resched())
                         cond_resched();
@@ -281,14 +279,17 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                 r = RESUME_GUEST;
                 break;
 
+        /* XXX move to a 440-specific file. */
         case BOOKE_INTERRUPT_DTLB_MISS: {
+                struct kvmppc_vcpu_44x *vcpu_44x = to_44x(vcpu);
                 struct kvmppc_44x_tlbe *gtlbe;
                 unsigned long eaddr = vcpu->arch.fault_dear;
+                int gtlb_index;
                 gfn_t gfn;
 
                 /* Check the guest TLB. */
-                gtlbe = kvmppc_44x_dtlb_search(vcpu, eaddr);
-                if (!gtlbe) {
+                gtlb_index = kvmppc_44x_dtlb_index(vcpu, eaddr);
+                if (gtlb_index < 0) {
                         /* The guest didn't have a mapping for it. */
                         kvmppc_booke_queue_irqprio(vcpu, BOOKE_IRQPRIO_DTLB_MISS);
                         vcpu->arch.dear = vcpu->arch.fault_dear;
@@ -298,6 +299,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                         break;
                 }
 
+                gtlbe = &vcpu_44x->guest_tlb[gtlb_index];
                 vcpu->arch.paddr_accessed = tlb_xlate(gtlbe, eaddr);
                 gfn = vcpu->arch.paddr_accessed >> PAGE_SHIFT;
 
@@ -309,7 +311,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                          * Either way, we need to satisfy the fault without
                          * invoking the guest. */
                         kvmppc_mmu_map(vcpu, eaddr, vcpu->arch.paddr_accessed, gtlbe->tid,
-                                       gtlbe->word2, get_tlb_bytes(gtlbe));
+                                       gtlbe->word2, get_tlb_bytes(gtlbe), gtlb_index);
                         vcpu->stat.dtlb_virt_miss_exits++;
                         r = RESUME_GUEST;
                 } else {
@@ -322,17 +324,20 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                 break;
         }
 
+        /* XXX move to a 440-specific file. */
         case BOOKE_INTERRUPT_ITLB_MISS: {
+                struct kvmppc_vcpu_44x *vcpu_44x = to_44x(vcpu);
                 struct kvmppc_44x_tlbe *gtlbe;
                 unsigned long eaddr = vcpu->arch.pc;
                 gpa_t gpaddr;
                 gfn_t gfn;
+                int gtlb_index;
 
                 r = RESUME_GUEST;
 
                 /* Check the guest TLB. */
-                gtlbe = kvmppc_44x_itlb_search(vcpu, eaddr);
-                if (!gtlbe) {
+                gtlb_index = kvmppc_44x_itlb_index(vcpu, eaddr);
+                if (gtlb_index < 0) {
                         /* The guest didn't have a mapping for it. */
                         kvmppc_booke_queue_irqprio(vcpu, BOOKE_IRQPRIO_ITLB_MISS);
                         vcpu->stat.itlb_real_miss_exits++;
@@ -341,6 +346,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 
                 vcpu->stat.itlb_virt_miss_exits++;
 
+                gtlbe = &vcpu_44x->guest_tlb[gtlb_index];
                 gpaddr = tlb_xlate(gtlbe, eaddr);
                 gfn = gpaddr >> PAGE_SHIFT;
 
@@ -352,7 +358,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                          * Either way, we need to satisfy the fault without
                          * invoking the guest. */
                         kvmppc_mmu_map(vcpu, eaddr, gpaddr, gtlbe->tid,
-                                       gtlbe->word2, get_tlb_bytes(gtlbe));
+                                       gtlbe->word2, get_tlb_bytes(gtlbe), gtlb_index);
                 } else {
                         /* Guest mapped and leaped at non-RAM! */
                         kvmppc_booke_queue_irqprio(vcpu, BOOKE_IRQPRIO_MACHINE_CHECK);