Subject: [PATCH v3 2/3] KVM: PPC: Book3S PR: Disallow AIL != 0

From: Nicholas Piggin <[email-masked]>
Date: Mon, 21 Feb 2022 17:23:52 +1000

KVM PR does not implement address translation modes on interrupt, so it
must not allow H_SET_MODE to succeed. The behaviour change caused by
this mode is architected and not advisory (interrupts *must* behave
differently).

QEMU does not deal with differences in AIL support in the host. The
solution to that is a spapr capability and corresponding KVM CAP, but
this patch does not break things more than before (the host behaviour
already differs, this change just disallows some modes that are not
implemented properly).

By happy coincidence, this allows PR Linux guests that are using the SCV
facility to boot and run, because Linux disables the use of SCV if AIL
can not be set to 3. This does not fix the underlying problem of missing
SCV support (an OS could implement real-mode SCV vectors and try to
enable the facility). The true fix for that is for KVM PR to emulate scv
interrupts from the facility unavailable interrupt.

Reviewed-by: Fabiano Rosas <[email-masked]>
Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kvm/book3s_pr_papr.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_pr_papr.c b/arch/powerpc/kvm/book3s_pr_papr.c
index 1f10e7dfcdd0..dc4f51ac84bc 100644
--- a/arch/powerpc/kvm/book3s_pr_papr.c
+++ b/arch/powerpc/kvm/book3s_pr_papr.c
@@ -281,6 +281,22 @@ static int kvmppc_h_pr_logical_ci_store(struct kvm_vcpu *vcpu)
 	return EMULATE_DONE;
 }
 
+static int kvmppc_h_pr_set_mode(struct kvm_vcpu *vcpu)
+{
+	unsigned long mflags = kvmppc_get_gpr(vcpu, 4);
+	unsigned long resource = kvmppc_get_gpr(vcpu, 5);
+
+	if (resource == H_SET_MODE_RESOURCE_ADDR_TRANS_MODE) {
+		/* KVM PR does not provide AIL!=0 to guests */
+		if (mflags == 0)
+			kvmppc_set_gpr(vcpu, 3, H_SUCCESS);
+		else
+			kvmppc_set_gpr(vcpu, 3, H_UNSUPPORTED_FLAG_START - 63);
+		return EMULATE_DONE;
+	}
+	return EMULATE_FAIL;
+}
+
 #ifdef CONFIG_SPAPR_TCE_IOMMU
 static int kvmppc_h_pr_put_tce(struct kvm_vcpu *vcpu)
 {
@@ -384,6 +400,8 @@ int kvmppc_h_pr(struct kvm_vcpu *vcpu, unsigned long cmd)
 		return kvmppc_h_pr_logical_ci_load(vcpu);
 	case H_LOGICAL_CI_STORE:
 		return kvmppc_h_pr_logical_ci_store(vcpu);
+	case H_SET_MODE:
+		return kvmppc_h_pr_set_mode(vcpu);
 	case H_XIRR:
 	case H_CPPR:
 	case H_EOI:
@@ -421,6 +439,7 @@ int kvmppc_hcall_impl_pr(unsigned long cmd)
 	case H_CEDE:
 	case H_LOGICAL_CI_LOAD:
 	case H_LOGICAL_CI_STORE:
+	case H_SET_MODE:
 #ifdef CONFIG_KVM_XICS
 	case H_XIRR:
 	case H_CPPR:
@@ -447,6 +466,7 @@ static unsigned int default_hcall_list[] = {
 	H_BULK_REMOVE,
 	H_PUT_TCE,
 	H_CEDE,
+	H_SET_MODE,
 #ifdef CONFIG_KVM_XICS
 	H_XIRR,
 	H_CPPR,
-- 
2.23.0