kvm_hstate.in_guest provides the equivalent of MSR[RI]=0 protection,
and it covers the existing MSR[RI]=0 section in late entry and early
exit, so clearing and setting MSR[RI] in those cases does not
actually do anything useful.
Remove the RI manipulation and replace it with comments. Make the
in_guest memory accesses a bit closer to a proper critical section
pattern. This speeds up guest entry/exit performance.
This also removes the MSR[RI] warnings which aren't very interesting
and would cause crashes if they hit due to causing an interrupt in
non-recoverable code.
From: Nicholas Piggin <npiggin@xxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv_p9_entry.c | 50 ++++++++++++---------------
1 file changed, 23 insertions(+), 27 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index cb865fe2580d..5745a49021c3 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -825,7 +825,15 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
* But TM could be split out if this would be a significant benefit.
*/
- local_paca->kvm_hstate.in_guest = KVM_GUEST_MODE_HV_P9;
+ /*
+ * MSR[RI] does not need to be cleared (and is not, for radix guests
+ * with no prefetch bug), because in_guest is set. If we take a SRESET
+ * or MCE with in_guest set but still in HV mode, then
+ * kvmppc_p9_bad_interrupt handles the interrupt, which effectively
+ * clears MSR[RI] and doesn't return.
+ */
+ WRITE_ONCE(local_paca->kvm_hstate.in_guest, KVM_GUEST_MODE_HV_P9);
+ barrier(); /* Open in_guest critical section */
/*
* Hash host, hash guest, or radix guest with prefetch bug, all have
@@ -837,14 +845,10 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
save_clear_host_mmu(kvm);
- if (kvm_is_radix(kvm)) {
+ if (kvm_is_radix(kvm))
switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
- if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
- __mtmsrd(0, 1); /* clear RI */
-
- } else {
+ else
switch_mmu_to_guest_hpt(kvm, vcpu, lpcr);
- }
/* TLBIEL uses LPID=LPIDR, so run this after setting guest LPID */
kvmppc_check_need_tlb_flush(kvm, vc->pcpu, nested);
@@ -899,19 +903,16 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
vcpu->arch.regs.gpr[3] = local_paca->kvm_hstate.scratch2;
/*
- * Only set RI after reading machine check regs (DAR, DSISR, SRR0/1)
- * and hstate scratch (which we need to move into exsave to make
- * re-entrant vs SRESET/MCE)
+ * After reading machine check regs (DAR, DSISR, SRR0/1) and hstate
+ * scratch (which we need to move into exsave to make re-entrant vs
+ * SRESET/MCE), register state is protected from reentrancy. However
+ * timebase, MMU, among other state is still set to guest, so don't
+ * enable MSR[RI] here. It gets enabled at the end, after in_guest
+ * is cleared.
+ *
+ * It is possible an NMI could come in here, which is why it is
+ * important to save the above state early so it can be debugged.
*/
- if (ri_set) {
- if (unlikely(!(mfmsr() & MSR_RI))) {
- __mtmsrd(MSR_RI, 1);
- WARN_ON_ONCE(1);
- }
- } else {
- WARN_ON_ONCE(mfmsr() & MSR_RI);
- __mtmsrd(MSR_RI, 1);
- }
vcpu->arch.regs.gpr[9] = exsave[EX_R9/sizeof(u64)];
vcpu->arch.regs.gpr[10] = exsave[EX_R10/sizeof(u64)];
@@ -969,13 +970,6 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
*/
mtspr(SPRN_HSRR0, vcpu->arch.regs.nip);
mtspr(SPRN_HSRR1, vcpu->arch.shregs.msr);
-
- /*
- * tm_return_to_guest re-loads SRR0/1, DAR,
- * DSISR after RI is cleared, in case they had
- * been clobbered by a MCE.
- */
- __mtmsrd(0, 1); /* clear RI */
goto tm_return_to_guest;
}
}
@@ -1075,7 +1069,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
restore_p9_host_os_sprs(vcpu, &host_os_sprs);
- local_paca->kvm_hstate.in_guest = KVM_GUEST_MODE_NONE;
+ barrier(); /* Close in_guest critical section */
+ WRITE_ONCE(local_paca->kvm_hstate.in_guest, KVM_GUEST_MODE_NONE);
+ /* Interrupts are recoverable at this point */
/*
* cp_abort is required if the processor supports local copy-paste
--
2.23.0
