KVM: arm64: Avoid storing the vcpu pointer on the stack

We already have the percpu area for the host cpu state, which points to
the VCPU, so there's no need to store the VCPU pointer on the stack on
every context switch.  We can be a little more clever and just use
tpidr_el2 for the percpu offset and load the VCPU pointer from the host
context.

This has the benefit of being able to retrieve the host context even
when our stack is corrupted, and it has a potential performance benefit
because we trade a store plus a load for an mrs and a load on a round
trip to the guest.

This does require us to calculate the percpu offset without including
the offset from the kernel mapping of the percpu array to the linear
mapping of the array (which is what we store in tpidr_el1), because a
PC-relative generated address in EL2 is already giving us the hyp alias
of the linear mapping of a kernel address.  We do this in
__cpu_init_hyp_mode() by using kvm_ksym_ref().

The code that accesses ESR_EL2 was previously using an alternative to
use the _EL1 accessor on VHE systems, but this was actually unnecessary
as the _EL1 accessor aliases the ESR_EL2 register on VHE, and the _EL2
accessor does the same thing on both systems.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

4 files changed, 17 insertions, 27 deletions

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index fdd1068ee3a5..1f458f7c3b44 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -62,9 +62,6 @@ ENTRY(__guest_enter)
 	// Store the host regs
 	save_callee_saved_regs x1
 
-	// Store host_ctxt and vcpu for use at exit time
-	stp	x1, x0, [sp, #-16]!
-
 	add	x18, x0, #VCPU_CONTEXT
 
 	// Restore guest regs x0-x17
@@ -118,8 +115,7 @@ ENTRY(__guest_exit)
 	// Store the guest regs x19-x29, lr
 	save_callee_saved_regs x1
 
-	// Restore the host_ctxt from the stack
-	ldr	x2, [sp], #16
+	get_host_ctxt	x2, x3
 
 	// Now restore the host regs
 	restore_callee_saved_regs x2
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f36464bd57c5..82fbc368f738 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -57,13 +57,8 @@ ENDPROC(__vhe_hyp_call)
 el1_sync:				// Guest trapped into EL2
 	stp	x0, x1, [sp, #-16]!
 
-alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
-	mrs	x1, esr_el2
-alternative_else
-	mrs	x1, esr_el1
-alternative_endif
-	lsr	x0, x1, #ESR_ELx_EC_SHIFT
-
+	mrs	x0, esr_el2
+	lsr	x0, x0, #ESR_ELx_EC_SHIFT
 	cmp	x0, #ESR_ELx_EC_HVC64
 	ccmp	x0, #ESR_ELx_EC_HVC32, #4, ne
 	b.ne	el1_trap
@@ -117,10 +112,14 @@ el1_hvc_guest:
 	eret
 
 el1_trap:
+	get_vcpu_ptr	x1, x0
+
+	mrs		x0, esr_el2
+	lsr		x0, x0, #ESR_ELx_EC_SHIFT
 	/*
 	 * x0: ESR_EC
+	 * x1: vcpu pointer
 	 */
-	ldr	x1, [sp, #16 + 8]	// vcpu stored by __guest_enter
 
 	/*
 	 * We trap the first access to the FP/SIMD to save the host context
@@ -138,13 +137,13 @@ alternative_else_nop_endif
 
 el1_irq:
 	stp     x0, x1, [sp, #-16]!
-	ldr	x1, [sp, #16 + 8]
+	get_vcpu_ptr	x1, x0
 	mov	x0, #ARM_EXCEPTION_IRQ
 	b	__guest_exit
 
 el1_error:
 	stp     x0, x1, [sp, #-16]!
-	ldr	x1, [sp, #16 + 8]
+	get_vcpu_ptr	x1, x0
 	mov	x0, #ARM_EXCEPTION_EL1_SERROR
 	b	__guest_exit
 
@@ -180,14 +179,7 @@ ENTRY(__hyp_do_panic)
 ENDPROC(__hyp_do_panic)
 
 ENTRY(__hyp_panic)
-	/*
-	 * '=kvm_host_cpu_state' is a host VA from the constant pool, it may
-	 * not be accessible by this address from EL2, hyp_panic() converts
-	 * it with kern_hyp_va() before use.
-	 */
-	ldr	x0, =kvm_host_cpu_state
-	mrs	x1, tpidr_el2
-	add	x0, x0, x1
+	get_host_ctxt x0, x1
 	b	hyp_panic
 ENDPROC(__hyp_panic)
 
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 24f52fedfb9e..46717da75643 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -469,7 +469,7 @@ static hyp_alternate_select(__hyp_call_panic,
 			    __hyp_call_panic_nvhe, __hyp_call_panic_vhe,
 			    ARM64_HAS_VIRT_HOST_EXTN);
 
-void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *__host_ctxt)
+void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)
 {
 	struct kvm_vcpu *vcpu = NULL;
 
@@ -478,9 +478,6 @@ void __hyp_text __noreturn hyp_panic(struct kvm_cpu_context *__host_ctxt)
 	u64 par = read_sysreg(par_el1);
 
 	if (read_sysreg(vttbr_el2)) {
-		struct kvm_cpu_context *host_ctxt;
-
-		host_ctxt = kern_hyp_va(__host_ctxt);
 		vcpu = host_ctxt->__hyp_running_vcpu;
 		__timer_disable_traps(vcpu);
 		__deactivate_traps(vcpu);
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 2c17afd2be96..43b7dd65e3e6 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -189,3 +189,8 @@ void __hyp_text __sysreg32_restore_state(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
 		write_sysreg(sysreg[DBGVCR32_EL2], dbgvcr32_el2);
 }
+
+void __hyp_text __kvm_set_tpidr_el2(u64 tpidr_el2)
+{
+	asm("msr tpidr_el2, %0": : "r" (tpidr_el2));
+}