On book3e, KVM uses load external pid (lwepx) dedicated instruction to read
guest last instruction on the exit path. lwepx exceptions (DTLB_MISS, DSI
and LRAT), generated by loading a guest address, needs to be handled by KVM.
These exceptions are generated in a substituted guest translation context
(EPLC[EGS] = 1) from host context (MSR[GS] = 0).
Currently, KVM hooks only interrupts generated from guest context (MSR[GS] = 1),
doing minimal checks on the fast path to avoid host performance degradation.
lwepx exceptions originate from host state (MSR[GS] = 0) which implies
additional checks in DO_KVM macro (beside the current MSR[GS] = 1) by looking
at the Exception Syndrome Register (ESR[EPID]) and the External PID Load Context
Register (EPLC[EGS]). Doing this on each Data TLB miss exception is obvious
too intrusive for the host.
Read guest last instruction from kvmppc_load_last_inst() by searching for the
physical address and kmap it. This address the TODO for TLB eviction and
execute-but-not-read entries, and allow us to get rid of lwepx until we are
able to handle failures.
A simple stress benchmark shows a 1% sys performance degradation compared with
previous approach (lwepx without failure handling):
time for i in `seq 1 10000`; do /bin/echo > /dev/null; done
real 0m 8.85s
user 0m 4.34s
sys 0m 4.48s
vs
real 0m 8.84s
user 0m 4.36s
sys 0m 4.44s
An alternative solution, to handle lwepx exceptions in KVM, is to temporary
highjack the interrupt vector from host. Some cores share host IVOR registers
between hardware threads, which is the case of FSL e6500, which impose additional
synchronization logic for this solution to work. The optimization can be addressed
later on top of this patch.
Signed-off-by: Mihai Caraman <mihai.caraman@xxxxxxxxxxxxx>
---
v4:
- add switch and new function when getting last inst earlier
- use enum instead of prev semnatic
- get rid of mas0, optimize mas7_mas3
- give more context in visible messages
- check storage attributes mismatch on MMUv2
- get rid of pfn_valid check
v3:
- reworked patch description
- use unaltered kmap addr for kunmap
- get last instruction before beeing preempted
v2:
- reworked patch description
- used pr_* functions
- addressed cosmetic feedback
arch/powerpc/kvm/booke.c | 44 +++++++++++++++++
arch/powerpc/kvm/bookehv_interrupts.S | 37 ++++----------
arch/powerpc/kvm/e500_mmu_host.c | 91 +++++++++++++++++++++++++++++++++++
3 files changed, 144 insertions(+), 28 deletions(-)
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 34a42b9..843077b 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -869,6 +869,28 @@ static void kvmppc_restart_interrupt(struct kvm_vcpu *vcpu,
}
}
+static int kvmppc_resume_inst_load(struct kvm_run *run, struct kvm_vcpu *vcpu,
+ enum emulation_result emulated, u32 last_inst)
+{
+ switch (emulated) {
+ case EMULATE_AGAIN:
+ return RESUME_GUEST;
+
+ case EMULATE_FAIL:
+ pr_debug("%s: load instruction from guest address %lx failed\n",
+ __func__, vcpu->arch.pc);
+ /* For debugging, encode the failing instruction and
+ * report it to userspace. */
+ run->hw.hardware_exit_reason = ~0ULL << 32;
+ run->hw.hardware_exit_reason |= last_inst;
+ kvmppc_core_queue_program(vcpu, ESR_PIL);
+ return RESUME_HOST;
+
+ default:
+ BUG();
+ }
+}
+
/**
* kvmppc_handle_exit
*
@@ -880,6 +902,8 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
int r = RESUME_HOST;
int s;
int idx;
+ u32 last_inst = KVM_INST_FETCH_FAILED;
+ enum emulation_result emulated = EMULATE_DONE;
/* update before a new last_exit_type is rewritten */
kvmppc_update_timing_stats(vcpu);
@@ -887,6 +911,20 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
/* restart interrupts if they were meant for the host */
kvmppc_restart_interrupt(vcpu, exit_nr);
+ /*
+ * get last instruction before beeing preempted
+ * TODO: for e6500 check also BOOKE_INTERRUPT_LRAT_ERROR & ESR_DATA
+ */
+ switch (exit_nr) {
+ case BOOKE_INTERRUPT_DATA_STORAGE:
+ case BOOKE_INTERRUPT_DTLB_MISS:
+ case BOOKE_INTERRUPT_HV_PRIV:
+ emulated = kvmppc_get_last_inst(vcpu, false, &last_inst);
+ break;
+ default:
+ break;
+ }
+
local_irq_enable();
trace_kvm_exit(exit_nr, vcpu);
@@ -895,6 +933,11 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
run->exit_reason = KVM_EXIT_UNKNOWN;
run->ready_for_interrupt_injection = 1;
+ if (emulated != EMULATE_DONE) {
+ r = kvmppc_resume_inst_load(run, vcpu, emulated, last_inst);
+ goto out;
+ }
+
switch (exit_nr) {
case BOOKE_INTERRUPT_MACHINE_CHECK:
printk("MACHINE CHECK: %lx\n", mfspr(SPRN_MCSR));
@@ -1184,6 +1227,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
BUG();
}
+out:
/*
* To avoid clobbering exit_reason, only check for signals if we
* aren't already exiting to userspace for some other reason.
diff --git a/arch/powerpc/kvm/bookehv_interrupts.S b/arch/powerpc/kvm/bookehv_interrupts.S
index 6ff4480..e000b39 100644
--- a/arch/powerpc/kvm/bookehv_interrupts.S
+++ b/arch/powerpc/kvm/bookehv_interrupts.S
@@ -121,38 +121,14 @@
1:
.if \flags & NEED_EMU
- /*
- * This assumes you have external PID support.
- * To support a bookehv CPU without external PID, you'll
- * need to look up the TLB entry and create a temporary mapping.
- *
- * FIXME: we don't currently handle if the lwepx faults. PR-mode
- * booke doesn't handle it either. Since Linux doesn't use
- * broadcast tlbivax anymore, the only way this should happen is
- * if the guest maps its memory execute-but-not-read, or if we
- * somehow take a TLB miss in the middle of this entry code and
- * evict the relevant entry. On e500mc, all kernel lowmem is
- * bolted into TLB1 large page mappings, and we don't use
- * broadcast invalidates, so we should not take a TLB miss here.
- *
- * Later we'll need to deal with faults here. Disallowing guest
- * mappings that are execute-but-not-read could be an option on
- * e500mc, but not on chips with an LRAT if it is used.
- */
-
- mfspr r3, SPRN_EPLC /* will already have correct ELPID and EGS */
PPC_STL r15, VCPU_GPR(R15)(r4)
PPC_STL r16, VCPU_GPR(R16)(r4)
PPC_STL r17, VCPU_GPR(R17)(r4)
PPC_STL r18, VCPU_GPR(R18)(r4)
PPC_STL r19, VCPU_GPR(R19)(r4)
- mr r8, r3
PPC_STL r20, VCPU_GPR(R20)(r4)
- rlwimi r8, r6, EPC_EAS_SHIFT - MSR_IR_LG, EPC_EAS
PPC_STL r21, VCPU_GPR(R21)(r4)
- rlwimi r8, r6, EPC_EPR_SHIFT - MSR_PR_LG, EPC_EPR
PPC_STL r22, VCPU_GPR(R22)(r4)
- rlwimi r8, r10, EPC_EPID_SHIFT, EPC_EPID
PPC_STL r23, VCPU_GPR(R23)(r4)
PPC_STL r24, VCPU_GPR(R24)(r4)
PPC_STL r25, VCPU_GPR(R25)(r4)
@@ -162,10 +138,15 @@
PPC_STL r29, VCPU_GPR(R29)(r4)
PPC_STL r30, VCPU_GPR(R30)(r4)
PPC_STL r31, VCPU_GPR(R31)(r4)
- mtspr SPRN_EPLC, r8
- isync
- lwepx r9, 0, r5
- mtspr SPRN_EPLC, r3
+
+ /*
+ * We don't use external PID support. lwepx faults would need to be
+ * handled by KVM and this implies aditional code in DO_KVM (for
+ * DTB_MISS, DSI and LRAT) to check ESR[EPID] and EPLC[EGS] which
+ * is too intrusive for the host. Get last instuction in
+ * kvmppc_get_last_inst().
+ */
+ li r9, KVM_INST_FETCH_FAILED
stw r9, VCPU_LAST_INST(r4)
.endif
diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c
index 4b4e8d6..57463e5 100644
--- a/arch/powerpc/kvm/e500_mmu_host.c
+++ b/arch/powerpc/kvm/e500_mmu_host.c
@@ -606,11 +606,102 @@ void kvmppc_mmu_map(struct kvm_vcpu *vcpu, u64 eaddr, gpa_t gpaddr,
}
}
+#ifdef CONFIG_KVM_BOOKE_HV
int kvmppc_load_last_inst(struct kvm_vcpu *vcpu, enum instruction_type type,
u32 *instr)
{
+ gva_t geaddr;
+ hpa_t addr;
+ hfn_t pfn;
+ hva_t eaddr;
+ u32 mas1, mas2, mas3;
+ u64 mas7_mas3;
+ struct page *page;
+ unsigned int addr_space, psize_shift;
+ bool pr;
+ unsigned long flags;
+
+ /* Search TLB for guest pc to get the real address */
+ geaddr = kvmppc_get_pc(vcpu);
+
+ addr_space = (vcpu->arch.shared->msr & MSR_IS) >> MSR_IR_LG;
+
+ local_irq_save(flags);
+ mtspr(SPRN_MAS6, (vcpu->arch.pid << MAS6_SPID_SHIFT) | addr_space);
+ mtspr(SPRN_MAS5, MAS5_SGS | vcpu->kvm->arch.lpid);
+ asm volatile("tlbsx 0, %[geaddr]\n" : :
+ [geaddr] "r" (geaddr));
+ mtspr(SPRN_MAS5, 0);
+ mtspr(SPRN_MAS8, 0);
+ mas1 = mfspr(SPRN_MAS1);
+ mas2 = mfspr(SPRN_MAS2);
+ mas3 = mfspr(SPRN_MAS3);
+#ifdef CONFIG_64BIT
+ mas7_mas3 = mfspr(SPRN_MAS7_MAS3);
+#else
+ mas7_mas3 = ((u64)mfspr(SPRN_MAS7) << 32) | mas3;
+#endif
+ local_irq_restore(flags);
+
+ /*
+ * If the TLB entry for guest pc was evicted, return to the guest.
+ * There are high chances to find a valid TLB entry next time.
+ */
+ if (!(mas1 & MAS1_VALID))
+ return EMULATE_AGAIN;
+
+ /*
+ * Another thread may rewrite the TLB entry in parallel, don't
+ * execute from the address if the execute permission is not set
+ */
+ pr = vcpu->arch.shared->msr & MSR_PR;
+ if (unlikely((pr && !(mas3 & MAS3_UX)) ||
+ (!pr && !(mas3 & MAS3_SX)))) {
+ pr_debug("%s: Instuction emulation from guest addres %08lx without execute permission\n",
+ __func__, geaddr);
+ return EMULATE_FAIL;
