linux-kernel - [RFC PATCH 1/2] Revert "KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1"

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Date: Thu, 27 Jun 2024 23:33:35 +0530
From: Gautam Menghani <gautam@...ux.ibm.com>
To: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        naveen.n.rao@...ux.ibm.com
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/2] Revert "KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1"

This reverts commit 7c3ded5735141ff4d049747c9f76672a8b737c49.

On PowerNV, when a nested guest tries to use a feature prohibited by
HFSCR, the nested hypervisor (L1) should get a H_FAC_UNAVAILABLE trap
and then L1 can emulate the feature. But with the change introduced by
commit 7c3ded573514 ("KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1")
the L1 ends up getting a H_EMUL_ASSIST because of which, the L1 ends up
injecting a SIGILL when L2 (nested guest) tries to use doorbells.

Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 31 ++-----------------------------
 1 file changed, 2 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index daaf7faf21a5..cea28ac05923 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -2052,36 +2052,9 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu *vcpu)
 		fallthrough; /* go to facility unavailable handler */
 #endif
 
-	case BOOK3S_INTERRUPT_H_FAC_UNAVAIL: {
-		u64 cause = vcpu->arch.hfscr >> 56;
-
-		/*
-		 * Only pass HFU interrupts to the L1 if the facility is
-		 * permitted but disabled by the L1's HFSCR, otherwise
-		 * the interrupt does not make sense to the L1 so turn
-		 * it into a HEAI.
-		 */
-		if (!(vcpu->arch.hfscr_permitted & (1UL << cause)) ||
-				(vcpu->arch.nested_hfscr & (1UL << cause))) {
-			ppc_inst_t pinst;
-			vcpu->arch.trap = BOOK3S_INTERRUPT_H_EMUL_ASSIST;
-
-			/*
-			 * If the fetch failed, return to guest and
-			 * try executing it again.
-			 */
-			r = kvmppc_get_last_inst(vcpu, INST_GENERIC, &pinst);
-			vcpu->arch.emul_inst = ppc_inst_val(pinst);
-			if (r != EMULATE_DONE)
-				r = RESUME_GUEST;
-			else
-				r = RESUME_HOST;
-		} else {
-			r = RESUME_HOST;
-		}
-
+	case BOOK3S_INTERRUPT_H_FAC_UNAVAIL:
+		r = RESUME_HOST;
 		break;
-	}
 
 	case BOOK3S_INTERRUPT_HV_RM_HARD:
 		vcpu->arch.trap = 0;
-- 
2.45.1