On 06/03/2021 02:06, Nicholas Piggin wrote:
LPCR[HDICE]=0 suppresses hypervisor decrementer exceptions on some
processors, so it must be enabled before HDEC is set.
Educating myself - is not it a processor bug when it does not suppress
hdec exceptions with HDICE=0?
Also, why do we want to enable interrupts before writing HDEC? Enabling
it may cause an interrupt right away a
Anyway whatever the answers are, this is not changed by this patch and
the change makes sense so
Reviewed-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
Rather than set it in the host LPCR then setting HDEC, move the HDEC
update to after the guest MMU context (including LPCR) is loaded.
There shouldn't be much concern with delaying HDEC by some 10s or 100s
of nanoseconds by setting it a bit later.
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 1f2ba8955c6a..ffde1917ab68 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3505,20 +3505,9 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
host_dawrx1 = mfspr(SPRN_DAWRX1);
}
- /*
- * P8 and P9 suppress the HDEC exception when LPCR[HDICE] = 0,
- * so set HDICE before writing HDEC.
- */
- mtspr(SPRN_LPCR, kvm->arch.host_lpcr | LPCR_HDICE);
- isync();
-
hdec = time_limit - mftb();
- if (hdec < 0) {
- mtspr(SPRN_LPCR, kvm->arch.host_lpcr);
- isync();
+ if (hdec < 0)
return BOOK3S_INTERRUPT_HV_DECREMENTER;
- }
- mtspr(SPRN_HDEC, hdec);
if (vc->tb_offset) {
u64 new_tb = mftb() + vc->tb_offset;
@@ -3564,6 +3553,12 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
+ /*
+ * P9 suppresses the HDEC exception when LPCR[HDICE] = 0,
+ * so set guest LPCR (with HDICE) before writing HDEC.
+ */
+ mtspr(SPRN_HDEC, hdec);
+
mtspr(SPRN_SRR0, vcpu->arch.shregs.srr0);
mtspr(SPRN_SRR1, vcpu->arch.shregs.srr1);
--
Alexey
