KVM: arm/arm64: Cleanup MMIO handling

Our MMIO handling is a bit odd, in the sense that it uses an
intermediate per-vcpu structure to store the various decoded
information that describe the access.

But the same information is readily available in the HSR/ESR_EL2
field, and we actually use this field to populate the structure.

Let's simplify the whole thing by getting rid of the superfluous
structure and save a (tiny) bit of space in the vcpu structure.

[32bit fix courtesy of Olof Johansson <olof@lixom.net>]
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm/include/asm/kvm_emulate.h

@@ -9,7 +9,6 @@
 
 #include <linux/kvm_host.h>
 #include <asm/kvm_asm.h>
-#include <asm/kvm_mmio.h>
 #include <asm/kvm_arm.h>
 #include <asm/cputype.h>
 
@@ -220,7 +219,7 @@ static inline bool kvm_vcpu_dabt_is_cm(struct kvm_vcpu *vcpu)
 }
 
 /* Get Access Size from a data abort */
-static inline int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu)
+static inline unsigned int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu)
 {
 	switch ((kvm_vcpu_get_hsr(vcpu) >> 22) & 0x3) {
 	case 0:
@@ -231,7 +230,7 @@ static inline int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu)
 		return 4;
 	default:
 		kvm_err("Hardware is weird: SAS 0b11 is reserved\n");
-		return -EFAULT;
+		return 4;
 	}
 }
 

arch/arm/include/asm/kvm_host.h

@@ -14,7 +14,6 @@
 #include <asm/cputype.h>
 #include <asm/kvm.h>
 #include <asm/kvm_asm.h>
-#include <asm/kvm_mmio.h>
 #include <asm/fpstate.h>
 #include <kvm/arm_arch_timer.h>
 
@@ -202,9 +201,6 @@ struct kvm_vcpu_arch {
 	 /* Don't run the guest (internal implementation need) */
 	bool pause;
 
-	/* IO related fields */
-	struct kvm_decode mmio_decode;
-
 	/* Cache some mmu pages needed inside spinlock regions */
 	struct kvm_mmu_memory_cache mmu_page_cache;
 
@@ -300,6 +296,14 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 static inline void handle_exit_early(struct kvm_vcpu *vcpu, struct kvm_run *run,
 				     int exception_index) {}
 
+/* MMIO helpers */
+void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
+unsigned long kvm_mmio_read_buf(const void *buf, unsigned int len);
+
+int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
+int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
+		 phys_addr_t fault_ipa);
+
 static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
 				       unsigned long hyp_stack_ptr,
 				       unsigned long vector_ptr)

arch/arm/include/asm/kvm_hyp.h

@@ -10,6 +10,7 @@
 #include <linux/compiler.h>
 #include <linux/kvm_host.h>
 #include <asm/cp15.h>
+#include <asm/kvm_arm.h>
 #include <asm/vfp.h>
 
 #define __hyp_text __section(.hyp.text) notrace

arch/arm/include/asm/kvm_mmio.h

-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2012 - Virtual Open Systems and Columbia University
- * Author: Christoffer Dall <c.dall@virtualopensystems.com>
- */
-
-#ifndef __ARM_KVM_MMIO_H__
-#define __ARM_KVM_MMIO_H__
-
-#include <linux/kvm_host.h>
-#include <asm/kvm_asm.h>
-#include <asm/kvm_arm.h>
-
-struct kvm_decode {
-	unsigned long rt;
-	bool sign_extend;
-	/* Not used on 32-bit arm */
-	bool sixty_four;
-};
-
-void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
-unsigned long kvm_mmio_read_buf(const void *buf, unsigned int len);
-
-int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
-int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
-		 phys_addr_t fault_ipa);
-
-#endif	/* __ARM_KVM_MMIO_H__ */

arch/arm64/include/asm/kvm_emulate.h

@@ -17,7 +17,6 @@
 #include <asm/esr.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_hyp.h>
-#include <asm/kvm_mmio.h>
 #include <asm/ptrace.h>
 #include <asm/cputype.h>
 #include <asm/virt.h>
@@ -341,7 +340,7 @@ static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu)
 	return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM);
 }
 
-static inline int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu)
+static inline unsigned int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu)
 {
 	return 1 << ((kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SAS) >> ESR_ELx_SAS_SHIFT);
 }

arch/arm64/include/asm/kvm_host.h

@@ -24,7 +24,6 @@
 #include <asm/fpsimd.h>
 #include <asm/kvm.h>
 #include <asm/kvm_asm.h>
-#include <asm/kvm_mmio.h>
 #include <asm/thread_info.h>
 
 #define __KVM_HAVE_ARCH_INTC_INITIALIZED
@@ -325,9 +324,6 @@ struct kvm_vcpu_arch {
 	/* Don't run the guest (internal implementation need) */
 	bool pause;
 
-	/* IO related fields */
-	struct kvm_decode mmio_decode;
-
 	/* Cache some mmu pages needed inside spinlock regions */
 	struct kvm_mmu_memory_cache mmu_page_cache;
 
@@ -491,6 +487,14 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 void handle_exit_early(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		       int exception_index);
 
+/* MMIO helpers */
+void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
+unsigned long kvm_mmio_read_buf(const void *buf, unsigned int len);
+
+int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
+int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
+		 phys_addr_t fault_ipa);
+
 int kvm_perf_init(void);
 int kvm_perf_teardown(void);
 

arch/arm64/include/asm/kvm_mmio.h

-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2012 - Virtual Open Systems and Columbia University
- * Author: Christoffer Dall <c.dall@virtualopensystems.com>
- */
-
-#ifndef __ARM64_KVM_MMIO_H__
-#define __ARM64_KVM_MMIO_H__
-
-#include <linux/kvm_host.h>
-#include <asm/kvm_arm.h>
-
-struct kvm_decode {
-	unsigned long rt;
-	bool sign_extend;
-	/* Witdth of the register accessed by the faulting instruction is 64-bits */
-	bool sixty_four;
-};
-
-void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
-unsigned long kvm_mmio_read_buf(const void *buf, unsigned int len);
-
-int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
-int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
-		 phys_addr_t fault_ipa);
-
-#endif	/* __ARM64_KVM_MMIO_H__ */

virt/kvm/arm/mmio.c

@@ -5,7 +5,6 @@
  */
 
 #include <linux/kvm_host.h>
-#include <asm/kvm_mmio.h>
 #include <asm/kvm_emulate.h>
 #include <trace/events/kvm.h>
 
@@ -92,26 +91,23 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
 	vcpu->mmio_needed = 0;
 
-	if (!run->mmio.is_write) {
-		len = run->mmio.len;
-		if (len > sizeof(unsigned long))
-			return -EINVAL;
-
+	if (!kvm_vcpu_dabt_iswrite(vcpu)) {
+		len = kvm_vcpu_dabt_get_as(vcpu);
 		data = kvm_mmio_read_buf(run->mmio.data, len);
 
-		if (vcpu->arch.mmio_decode.sign_extend &&
+		if (kvm_vcpu_dabt_issext(vcpu) &&
 		    len < sizeof(unsigned long)) {
 			mask = 1U << ((len * 8) - 1);
 			data = (data ^ mask) - mask;
 		}
 
-		if (!vcpu->arch.mmio_decode.sixty_four)
+		if (!kvm_vcpu_dabt_issf(vcpu))
 			data = data & 0xffffffff;
 
 		trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
 			       &data);
 		data = vcpu_data_host_to_guest(vcpu, data, len);
-		vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data);
+		vcpu_set_reg(vcpu, kvm_vcpu_dabt_get_rd(vcpu), data);
 	}
 
 	/*
@@ -123,36 +119,6 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	return 0;
 }
 
-static int decode_hsr(struct kvm_vcpu *vcpu, bool *is_write, int *len)
-{
-	unsigned long rt;
-	int access_size;
-	bool sign_extend;
-	bool sixty_four;
-
-	if (kvm_vcpu_dabt_iss1tw(vcpu)) {
-		/* page table accesses IO mem: tell guest to fix its TTBR */
-		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
-		return 1;
-	}
-
-	access_size = kvm_vcpu_dabt_get_as(vcpu);
-	if (unlikely(access_size < 0))
-		return access_size;
-
-	*is_write = kvm_vcpu_dabt_iswrite(vcpu);
-	sign_extend = kvm_vcpu_dabt_issext(vcpu);
-	sixty_four = kvm_vcpu_dabt_issf(vcpu);
-	rt = kvm_vcpu_dabt_get_rd(vcpu);
-
-	*len = access_size;
-	vcpu->arch.mmio_decode.sign_extend = sign_extend;
-	vcpu->arch.mmio_decode.rt = rt;
-	vcpu->arch.mmio_decode.sixty_four = sixty_four;
-
-	return 0;
-}
-
 int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		 phys_addr_t fault_ipa)
 {
@@ -164,15 +130,10 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	u8 data_buf[8];
 
 	/*
-	 * Prepare MMIO operation. First decode the syndrome data we get
-	 * from the CPU. Then try if some in-kernel emulation feels
-	 * responsible, otherwise let user space do its magic.
+	 * No valid syndrome? Ask userspace for help if it has
+	 * voluntered to do so, and bail out otherwise.
 	 */
-	if (kvm_vcpu_dabt_isvalid(vcpu)) {
-		ret = decode_hsr(vcpu, &is_write, &len);
-		if (ret)
-			return ret;
-	} else {
+	if (!kvm_vcpu_dabt_isvalid(vcpu)) {
 		if (vcpu->kvm->arch.return_nisv_io_abort_to_user) {
 			run->exit_reason = KVM_EXIT_ARM_NISV;
 			run->arm_nisv.esr_iss = kvm_vcpu_dabt_iss_nisv_sanitized(vcpu);
@@ -184,7 +145,20 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		return -ENOSYS;
 	}
 
-	rt = vcpu->arch.mmio_decode.rt;
+	/* Page table accesses IO mem: tell guest to fix its TTBR */
+	if (kvm_vcpu_dabt_iss1tw(vcpu)) {
+		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
+		return 1;
+	}
+
+	/*
+	 * Prepare MMIO operation. First decode the syndrome data we get
+	 * from the CPU. Then try if some in-kernel emulation feels
+	 * responsible, otherwise let user space do its magic.
+	 */
+	is_write = kvm_vcpu_dabt_iswrite(vcpu);
+	len = kvm_vcpu_dabt_get_as(vcpu);
+	rt = kvm_vcpu_dabt_get_rd(vcpu);
 
 	if (is_write) {
 		data = vcpu_data_guest_to_host(vcpu, vcpu_get_reg(vcpu, rt),

virt/kvm/arm/mmu.c

@@ -14,7 +14,6 @@
 #include <asm/cacheflush.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_mmu.h>
-#include <asm/kvm_mmio.h>
 #include <asm/kvm_ras.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>