[PATCH] KVM: arm64: Fix nVHE hyp panic host context restore

[Andrew Scull <ascull@xxxxxxxxxx>]

Commit c4b000c3928d4f20acef79dccf3a65ae3795e0b0 upstream.

When panicking from the nVHE hyp and restoring the host context, x29 is
expected to hold a pointer to the host context. This wasn't being done
so fix it to make sure there's a valid pointer the host context being
used.

Rather than passing a boolean indicating whether or not the host context
should be restored, instead pass the pointer to the host context. NULL
is passed to indicate that no context should be restored.

Fixes: a2e102e20fd6 ("KVM: arm64: nVHE: Handle hyp panics")
Cc: stable@xxxxxxxxxxxxxxx # 5.10.y only
Signed-off-by: Andrew Scull <ascull@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210219122406.1337626-1-ascull@xxxxxxxxxx
---
 arch/arm64/include/asm/kvm_hyp.h |  3 ++-
 arch/arm64/kvm/hyp/nvhe/host.S   | 20 ++++++++++----------
 arch/arm64/kvm/hyp/nvhe/switch.c |  3 +--
 3 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
index 6b664de5ec1f..183bc9c7e1cb 100644
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -94,7 +94,8 @@ u64 __guest_enter(struct kvm_vcpu *vcpu);
 
 void __noreturn hyp_panic(void);
 #ifdef __KVM_NVHE_HYPERVISOR__
-void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
+void __noreturn __hyp_do_panic(struct kvm_cpu_context *host_ctxt, u64 spsr,
+			       u64 elr, u64 par);
 #endif
 
 #endif /* __ARM64_KVM_HYP_H__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index ed27f06a31ba..4ce934fc1f72 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -64,10 +64,15 @@ __host_enter_without_restoring:
 SYM_FUNC_END(__host_exit)
 
 /*
- * void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
+ * void __noreturn __hyp_do_panic(struct kvm_cpu_context *host_ctxt, u64 spsr,
+ * 				  u64 elr, u64 par);
  */
 SYM_FUNC_START(__hyp_do_panic)
-	/* Load the format arguments into x1-7 */
+	mov	x29, x0
+
+	/* Load the format string into x0 and arguments into x1-7 */
+	ldr	x0, =__hyp_panic_string
+
 	mov	x6, x3
 	get_vcpu_ptr x7, x3
 
@@ -82,13 +87,8 @@ SYM_FUNC_START(__hyp_do_panic)
 	ldr	lr, =panic
 	msr	elr_el2, lr
 
-	/*
-	 * Set the panic format string and enter the host, conditionally
-	 * restoring the host context.
-	 */
-	cmp	x0, xzr
-	ldr	x0, =__hyp_panic_string
-	b.eq	__host_enter_without_restoring
+	/* Enter the host, conditionally restoring the host context. */
+	cbz	x29, __host_enter_without_restoring
 	b	__host_enter_for_panic
 SYM_FUNC_END(__hyp_do_panic)
 
@@ -144,7 +144,7 @@ SYM_FUNC_END(__hyp_do_panic)
 
 .macro invalid_host_el1_vect
 	.align 7
-	mov	x0, xzr		/* restore_host = false */
+	mov	x0, xzr		/* host_ctxt = NULL */
 	mrs	x1, spsr_el2
 	mrs	x2, elr_el2
 	mrs	x3, par_el1
diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 8ae8160bc93a..1b16a3457e2b 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -251,7 +251,6 @@ void __noreturn hyp_panic(void)
 	u64 spsr = read_sysreg_el2(SYS_SPSR);
 	u64 elr = read_sysreg_el2(SYS_ELR);
 	u64 par = read_sysreg_par();
-	bool restore_host = true;
 	struct kvm_cpu_context *host_ctxt;
 	struct kvm_vcpu *vcpu;
 
@@ -265,7 +264,7 @@ void __noreturn hyp_panic(void)
 		__sysreg_restore_state_nvhe(host_ctxt);
 	}
 
-	__hyp_do_panic(restore_host, spsr, elr, par);
+	__hyp_do_panic(host_ctxt, spsr, elr, par);
 	unreachable();
 }
 
-- 
2.31.0.rc2.261.g7f71774620-goog