diff mbox series

[v1,1/2] KVM: PPC: Book3S HV P9: Move setting HDEC after switching to guest LPCR

Message ID 20210413134223.1691892-2-npiggin@gmail.com
State New
Headers show
Series KVM: PPC: timer improvements | expand

Checks

Context Check Description
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (d02429becbe77bc4d27a7357afaf28f9294945bb)
snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 33 lines checked
snowpatch_ozlabs/needsstable success Patch has no Fixes tags

Commit Message

Nicholas Piggin April 13, 2021, 1:42 p.m. UTC
LPCR[HDICE]=0 suppresses hypervisor decrementer exceptions on some
processors, so it must be enabled before HDEC is set.

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.

Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)
diff mbox series

Patch

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 981bcaf787a8..48df339affdf 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3502,20 +3502,9 @@  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, vcpu->kvm->arch.host_lpcr | LPCR_HDICE);
-	isync();
-
 	hdec = time_limit - mftb();
-	if (hdec < 0) {
-		mtspr(SPRN_LPCR, vcpu->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;
@@ -3563,6 +3552,12 @@  static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
 	mtspr(SPRN_LPCR, lpcr);
 	isync();
 
+	/*
+	 * P9 suppresses the HDEC exception when LPCR[HDICE] = 0,
+	 * so set guest LPCR (with HDICE) before writing HDEC.
+	 */
+	mtspr(SPRN_HDEC, hdec);
+
 	kvmppc_xive_push_vcpu(vcpu);
 
 	mtspr(SPRN_SRR0, vcpu->arch.shregs.srr0);