[PATCH 16/37] KVM: arm64: nVHE: Handle stub HVCs in the host loop

[Andrew Scull <ascull@google.com>]

Since the host is called from the hyp run loop, we can use that context
to identify calls from the host rather than checking VTTBR_EL2, which
will be used for the host's stage 2 in future.

Moving this to C also allows for more flexibiliy e.g. in applying
policies, such as forbidding HVC_RESET_VECTORS, based on the current
state of the hypervisor and removes the special casing for nVHE in the
exception handler.

Control over arch workaround 2 is made available to the host, the same
as any other vcpu.

Signed-off-by: Andrew Scull <ascull@google.com>
---
 arch/arm64/kvm/hyp/hyp-entry.S     | 36 ++-------------------
 arch/arm64/kvm/hyp/nvhe/hyp-init.S | 15 +++++++--
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 50 +++++++++++++++++++++++++++++-
 3 files changed, 65 insertions(+), 36 deletions(-)

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index a45459d1c135..3113665ce912 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -17,50 +17,20 @@
 
 	.text
 
-el1_sync:				// Guest trapped into EL2
-
+el1_sync:
 	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
 
-#ifdef __KVM_NVHE_HYPERVISOR__
-	mrs	x1, vttbr_el2		// If vttbr is valid, the guest
-	cbnz	x1, el1_hvc_guest	// called HVC
-
-	/* Here, we're pretty sure the host called HVC. */
-	ldp	x0, x1, [sp]
-
-	/* Check for a stub HVC call */
-	cmp	x0, #HVC_STUB_HCALL_NR
-	b.hs	el1_trap
-	add	sp, sp, #16
-
-	/*
-	 * Compute the idmap address of __kvm_handle_stub_hvc and
-	 * jump there. Since we use kimage_voffset, do not use the
-	 * HYP VA for __kvm_handle_stub_hvc, but the kernel VA instead
-	 * (by loading it from the constant pool).
-	 *
-	 * Preserve x0-x4, which may contain stub parameters.
-	 */
-	ldr	x5, =__kvm_handle_stub_hvc
-	ldr_l	x6, kimage_voffset
-
-	/* x5 = __pa(x5) */
-	sub	x5, x5, x6
-	br	x5
-#endif /* __KVM_NVHE_HYPERVISOR__ */
-
-el1_hvc_guest:
 	/*
 	 * Fastest possible path for ARM_SMCCC_ARCH_WORKAROUND_1.
 	 * The workaround has already been applied on the host,
 	 * so let's quickly get back to the guest. We don't bother
 	 * restoring x1, as it can be clobbered anyway.
 	 */
-	ldr	x1, [sp]				// Guest's x0
+	ldr	x1, [sp]				// vcpu's x0
 	eor	w1, w1, #ARM_SMCCC_ARCH_WORKAROUND_1
 	cbz	w1, wa_epilogue
 
@@ -77,7 +47,7 @@ alternative_cb_end
 	ldr	x0, [x2, #VCPU_WORKAROUND_FLAGS]
 
 	// Sanitize the argument and update the guest flags
-	ldr	x1, [sp, #8]			// Guest's x1
+	ldr	x1, [sp, #8]			// vcpu's x1
 	clz	w1, w1				// Murphy's device:
 	lsr	w1, w1, #5			// w1 = !!w1 without using
 	eor	w1, w1, #1			// the flags...
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index df2a7904a83b..43e1ee6178d4 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -15,6 +15,9 @@
 #include <asm/sysreg.h>
 #include <asm/virt.h>
 
+#include <asm/kvm_asm.h>
+#include <asm/kvm_ptrauth.h>
+
 	.text
 	.pushsection	.hyp.idmap.text, "ax"
 
@@ -137,6 +140,7 @@ SYM_CODE_START(__kvm_handle_stub_hvc)
 	cmp	x0, #HVC_SOFT_RESTART
 	b.ne	1f
 
+SYM_INNER_LABEL(__kvm_handle_stub_hvc_soft_restart, SYM_L_GLOBAL)
 	/* This is where we're about to jump, staying at EL2 */
 	msr	elr_el2, x1
 	mov	x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT | PSR_MODE_EL2h)
@@ -146,11 +150,18 @@ SYM_CODE_START(__kvm_handle_stub_hvc)
 	mov	x0, x2
 	mov	x1, x3
 	mov	x2, x4
-	b	reset
+	b	2f
 
 1:	cmp	x0, #HVC_RESET_VECTORS
 	b.ne	1f
-reset:
+
+SYM_INNER_LABEL(__kvm_handle_stub_hvc_reset_vectors, SYM_L_GLOBAL)
+	/* Restore host's ptrauth, sp_el0 and callee saved regs */
+	ptrauth_switch_to_guest x5, x6, x7, x8
+	restore_sp_el0 x5, x6
+	restore_callee_saved_regs x5
+
+2:
 	/*
 	 * Reset kvm back to the hyp stub. Do not clobber x0-x4 in
 	 * case we coming via HVC_SOFT_RESTART.
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 213977634601..d013586e3a03 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -13,6 +13,51 @@
 
 #include <kvm/arm_hypercalls.h>
 
+typedef unsigned long (*stub_hvc_handler_t)
+	(unsigned long, unsigned long, unsigned long, unsigned long,
+	 unsigned long, struct kvm_cpu_context *);
+
+extern char __kvm_handle_stub_hvc_soft_restart[];
+extern char __kvm_handle_stub_hvc_reset_vectors[];
+
+static void handle_stub_hvc(unsigned long func_id, struct kvm_vcpu *host_vcpu)
+{
+	char *stub_hvc_handler_kern_va;
+	__noreturn stub_hvc_handler_t stub_hvc_handler;
+
+	/*
+	 * The handlers of the supported stub HVCs disable the MMU so they must
+	 * be called in the idmap. We compute the idmap address by subtracting
+	 * kimage_voffset from the kernel VA handler.
+	 */
+	switch (func_id) {
+	case HVC_SOFT_RESTART:
+		asm volatile("ldr %0, =%1"
+			     : "=r" (stub_hvc_handler_kern_va)
+			     : "S" (__kvm_handle_stub_hvc_soft_restart));
+		break;
+	case HVC_RESET_VECTORS:
+		asm volatile("ldr %0, =%1"
+			     : "=r" (stub_hvc_handler_kern_va)
+			     : "S" (__kvm_handle_stub_hvc_reset_vectors));
+		break;
+	default:
+		vcpu_set_reg(host_vcpu, 0, HVC_STUB_ERR);
+		return;
+	}
+
+	stub_hvc_handler = (__noreturn stub_hvc_handler_t)
+		(stub_hvc_handler_kern_va - kimage_voffset);
+
+	/* Preserve x0-x4, which may contain stub parameters. */
+	stub_hvc_handler(func_id,
+			 vcpu_get_reg(host_vcpu, 1),
+			 vcpu_get_reg(host_vcpu, 2),
+			 vcpu_get_reg(host_vcpu, 3),
+			 vcpu_get_reg(host_vcpu, 4),
+			 &host_vcpu->arch.ctxt);
+}
+
 static void handle_host_hcall(unsigned long func_id, struct kvm_vcpu *host_vcpu)
 {
 	unsigned long ret = 0;
@@ -105,7 +150,10 @@ static void handle_trap(struct kvm_vcpu *host_vcpu) {
 	if (kvm_vcpu_trap_get_class(host_vcpu) == ESR_ELx_EC_HVC64) {
 		unsigned long func_id = smccc_get_function(host_vcpu);
 
-		handle_host_hcall(func_id, host_vcpu);
+		if (func_id < HVC_STUB_HCALL_NR)
+			handle_stub_hvc(func_id, host_vcpu);
+		else
+			handle_host_hcall(func_id, host_vcpu);
 	}
 
 	/* Other traps are ignored. */
-- 
2.27.0.389.gc38d7665816-goog

_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm