Tighten up partition switching code synchronisation and comments.
In particular, hwsync ; isync is required after the last access that is
performed in the context of a partition, before the partition is
switched away from.
-301 cycles (6319) POWER9 virt-mode NULL hcall
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
arch/powerpc/kvm/book3s_64_mmu_radix.c | 4 +++
arch/powerpc/kvm/book3s_hv_p9_entry.c | 40 +++++++++++++++++++-------
2 files changed, 33 insertions(+), 11 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index b5905ae4377c..c5508744e14c 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -54,6 +54,8 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
preempt_disable();
+ asm volatile("hwsync" ::: "memory");
+ isync();
/* switch the lpid first to avoid running host with unallocated pid */
old_lpid = mfspr(SPRN_LPID);
if (old_lpid != lpid)
@@ -70,6 +72,8 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
else
ret = copy_to_user_nofault((void __user *)to, from, n);
+ asm volatile("hwsync" ::: "memory");
+ isync();
/* switch the pid first to avoid running host with unallocated pid */
if (quadrant == 1 && pid != old_pid)
mtspr(SPRN_PID, old_pid);
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 5fca0a09425d..0aad2bf29d6e 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -521,17 +521,19 @@ static void switch_mmu_to_guest_radix(struct kvm *kvm, struct kvm_vcpu *vcpu, u6
lpid = nested ? nested->shadow_lpid : kvm->arch.lpid;
/*
- * All the isync()s are overkill but trivially follow the ISA
- * requirements. Some can likely be replaced with justification
- * comment for why they are not needed.
+ * Prior memory accesses to host PID Q3 must be completed before we
+ * start switching, and stores must be drained to avoid not-my-LPAR
+ * logic (see switch_mmu_to_host).
*/
+ asm volatile("hwsync" ::: "memory");
isync();
mtspr(SPRN_LPID, lpid);
- isync();
mtspr(SPRN_LPCR, lpcr);
- isync();
mtspr(SPRN_PID, vcpu->arch.pid);
- isync();
+ /*
+ * isync not required here because we are HRFID'ing to guest before
+ * any guest context access, which is context synchronising.
+ */
}
static void switch_mmu_to_guest_hpt(struct kvm *kvm, struct kvm_vcpu *vcpu, u64 lpcr)
@@ -541,25 +543,41 @@ static void switch_mmu_to_guest_hpt(struct kvm *kvm, struct kvm_vcpu *vcpu, u64
lpid = kvm->arch.lpid;
+ /*
+ * See switch_mmu_to_guest_radix. ptesync should not be required here
+ * even if the host is in HPT mode because speculative accesses would
+ * not cause RC updates (we are in real mode).
+ */
+ asm volatile("hwsync" ::: "memory");
+ isync();
mtspr(SPRN_LPID, lpid);
mtspr(SPRN_LPCR, lpcr);
mtspr(SPRN_PID, vcpu->arch.pid);
for (i = 0; i < vcpu->arch.slb_max; i++)
mtslb(vcpu->arch.slb[i].orige, vcpu->arch.slb[i].origv);
-
- isync();
+ /*
+ * isync not required here, see switch_mmu_to_guest_radix.
+ */
}
static void switch_mmu_to_host(struct kvm *kvm, u32 pid)
{
+ /*
+ * The guest has exited, so guest MMU context is no longer being
+ * non-speculatively accessed, but a hwsync is needed before the
+ * mtLPIDR / mtPIDR switch, in order to ensure all stores are drained,
+ * so the not-my-LPAR tlbie logic does not overlook them.
+ */
+ asm volatile("hwsync" ::: "memory");
isync();
mtspr(SPRN_PID, pid);
- isync();
mtspr(SPRN_LPID, kvm->arch.host_lpid);
- isync();
mtspr(SPRN_LPCR, kvm->arch.host_lpcr);
- isync();
+ /*
+ * isync is not required after the switch, because mtmsrd with L=0
+ * is performed after this switch, which is context synchronising.
+ */
if (!radix_enabled())
slb_restore_bolted_realmode();
--
2.23.0
