[PATCH AUTOSEL 5.15 26/37] KVM: PPC: Book3S HV Nested: L2 LPCR should inherit L1 LPES setting

[Sasha Levin]

From: Nicholas Piggin <npiggin at gmail.com>

[ Upstream commit 2852ebfa10afdcefff35ec72c8da97141df9845c ]

The L1 should not be able to adjust LPES mode for the L2. Setting LPES
if the L0 needs it clear would cause external interrupts to be sent to
L2 and missed by the L0.

Clearing LPES when it may be set, as typically happens with XIVE enabled
could cause a performance issue despite having no native XIVE support in
the guest, because it will cause mediated interrupts for the L2 to be
taken in HV mode, which then have to be injected.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
Reviewed-by: Fabiano Rosas <farosas at linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Link: https://lore.kernel.org/r/20220303053315.1056880-7-npiggin@gmail.com
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 arch/powerpc/kvm/book3s_hv.c        | 4 ++++
 arch/powerpc/kvm/book3s_hv_nested.c | 3 +--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 7fa685711669..eba77096c443 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -5235,6 +5235,10 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
 		kvm->arch.host_lpcr = lpcr = mfspr(SPRN_LPCR);
 		lpcr &= LPCR_PECE | LPCR_LPES;
 	} else {
+		/*
+		 * The L2 LPES mode will be set by the L0 according to whether
+		 * or not it needs to take external interrupts in HV mode.
+		 */
 		lpcr = 0;
 	}
 	lpcr |= (4UL << LPCR_DPFD_SH) | LPCR_HDICE |
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 6c4e0e93105f..ddea14e5cb5e 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -261,8 +261,7 @@ static void load_l2_hv_regs(struct kvm_vcpu *vcpu,
 	/*
 	 * Don't let L1 change LPCR bits for the L2 except these:
 	 */
-	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_AIL | LPCR_LD |
-		LPCR_LPES | LPCR_MER;
+	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_AIL | LPCR_LD | LPCR_MER;
 
 	/*
 	 * Additional filtering is required depending on hardware
-- 
2.35.1