[RFC 1/3] KVM: PPC: Book3S HV: Read EX_DSISR as a 32-bit field on guest exit

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

kvmhv_vcpu_entry_p9() recovers the guest fault state from the paca
exception save area with

	vcpu->arch.fault_dsisr = exsave[EX_DSISR/sizeof(u64)];

but EX_DSISR is not a doubleword. It is a 32-bit field at offset 48 that
shares a doubleword with EX_CCR at offset 52 and the exception entry in
exceptions-64s.S stores it accordingly. For e.g.

	stw	r10,IAREA+EX_DSISR(r13)

This issue was caught when running kvm selftests on big-endian, where
this read would land in the high half and the truncation yields EX_CCR
instead - KVM acts on the guest's condition register as if it were
HDSISR.

The result is that every HDSI on a big-endian host is evaluated against a
bogus fault status i.e. it fails with below error:

	KVM: Got radix HV page fault with DSISR=84004840

Let's fix this by reading this field at it's natural width.

Fixes: 89d35b239101 ("KVM: PPC: Book3S HV P9: Implement the rest of the P9 path in C")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 34bc0a8a1288..16aa8582b888 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -529,6 +529,15 @@ unsigned long kvmppc_msr_hard_disable_set_facilities(struct kvm_vcpu *vcpu, unsi
 }
 EXPORT_SYMBOL_GPL(kvmppc_msr_hard_disable_set_facilities);
 
+/*
+ * EX_DSISR is a 32-bit field that shares a doubleword with EX_CCR.
+ * Small helper for reading it back at its natural width.
+ */
+static u32 exsave_dsisr(u64 *exsave)
+{
+	return *(u32 *)((void *)exsave + EX_DSISR);
+}
+
 int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpcr, u64 *tb)
 {
 	struct p9_host_os_sprs host_os_sprs;
@@ -770,7 +779,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	if (unlikely(trap == BOOK3S_INTERRUPT_MACHINE_CHECK)) {
 		vcpu->arch.fault_dar = exsave[EX_DAR/sizeof(u64)];
-		vcpu->arch.fault_dsisr = exsave[EX_DSISR/sizeof(u64)];
+		vcpu->arch.fault_dsisr = exsave_dsisr(exsave);
 		kvmppc_realmode_machine_check(vcpu);
 
 	} else if (unlikely(trap == BOOK3S_INTERRUPT_HMI)) {
@@ -781,7 +790,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	} else if (trap == BOOK3S_INTERRUPT_H_DATA_STORAGE) {
 		vcpu->arch.fault_dar = exsave[EX_DAR/sizeof(u64)];
-		vcpu->arch.fault_dsisr = exsave[EX_DSISR/sizeof(u64)];
+		vcpu->arch.fault_dsisr = exsave_dsisr(exsave);
 		vcpu->arch.fault_gpa = mfspr(SPRN_ASDR);
 
 	} else if (trap == BOOK3S_INTERRUPT_H_INST_STORAGE) {
-- 
2.39.5