Re: [PATCH v2 4/5] KVM: selftests: Add exception handling support for aarch64

[Ricardo Koller <ricarkol@google.com>]

On Mon, May 03, 2021 at 11:32:39AM +0100, Marc Zyngier wrote:
> On Sat, 01 May 2021 00:24:06 +0100,
> Ricardo Koller <ricarkol@google.com> wrote:
> > 
> > Add the infrastructure needed to enable exception handling in aarch64
> > selftests. The exception handling defaults to an unhandled-exception
> > handler which aborts the test, just like x86. These handlers can be
> > overridden by calling vm_install_vector_handler(vector) or
> > vm_install_exception_handler(vector, ec). The unhandled exception
> > reporting from the guest is done using the ucall type introduced in a
> > previous commit, UCALL_UNHANDLED.
> > 
> > The exception handling code is heavily inspired on kvm-unit-tests.
> > 
> > Signed-off-by: Ricardo Koller <ricarkol@google.com>
> > ---
> >  tools/testing/selftests/kvm/Makefile          |   2 +-
> >  .../selftests/kvm/include/aarch64/processor.h |  78 +++++++++++
> >  .../selftests/kvm/lib/aarch64/handlers.S      | 130 ++++++++++++++++++
> >  .../selftests/kvm/lib/aarch64/processor.c     | 124 +++++++++++++++++
> >  4 files changed, 333 insertions(+), 1 deletion(-)
> >  create mode 100644 tools/testing/selftests/kvm/lib/aarch64/handlers.S
> > 
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index 4e548d7ab0ab..618c5903f478 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -35,7 +35,7 @@ endif
> >  
> >  LIBKVM = lib/assert.c lib/elf.c lib/io.c lib/kvm_util.c lib/sparsebit.c lib/test_util.c lib/guest_modes.c lib/perf_test_util.c
> >  LIBKVM_x86_64 = lib/x86_64/processor.c lib/x86_64/vmx.c lib/x86_64/svm.c lib/x86_64/ucall.c lib/x86_64/handlers.S
> > -LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c
> > +LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handlers.S
> >  LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
> >  
> >  TEST_GEN_PROGS_x86_64 = x86_64/cr4_cpuid_sync_test
> > diff --git a/tools/testing/selftests/kvm/include/aarch64/processor.h b/tools/testing/selftests/kvm/include/aarch64/processor.h
> > index b7fa0c8551db..40aae31b4afc 100644
> > --- a/tools/testing/selftests/kvm/include/aarch64/processor.h
> > +++ b/tools/testing/selftests/kvm/include/aarch64/processor.h
> > @@ -8,6 +8,7 @@
> >  #define SELFTEST_KVM_PROCESSOR_H
> >  
> >  #include "kvm_util.h"
> > +#include <linux/stringify.h>
> >  
> >  
> >  #define ARM64_CORE_REG(x) (KVM_REG_ARM64 | KVM_REG_SIZE_U64 | \
> > @@ -18,6 +19,7 @@
> >  #define MAIR_EL1	3, 0, 10, 2, 0
> >  #define TTBR0_EL1	3, 0,  2, 0, 0
> >  #define SCTLR_EL1	3, 0,  1, 0, 0
> > +#define VBAR_EL1	3, 0, 12, 0, 0
> >  
> >  /*
> >   * Default MAIR
> > @@ -56,4 +58,80 @@ void aarch64_vcpu_setup(struct kvm_vm *vm, int vcpuid, struct kvm_vcpu_init *ini
> >  void aarch64_vcpu_add_default(struct kvm_vm *vm, uint32_t vcpuid,
> >  			      struct kvm_vcpu_init *init, void *guest_code);
> >  
> > +struct ex_regs {
> > +	u64 regs[31];
> > +	u64 sp;
> > +	u64 pc;
> > +	u64 pstate;
> > +};
> > +
> > +#define VECTOR_NUM	16
> > +
> > +enum {
> > +	VECTOR_SYNC_CURRENT_SP0,
> > +	VECTOR_IRQ_CURRENT_SP0,
> > +	VECTOR_FIQ_CURRENT_SP0,
> > +	VECTOR_ERROR_CURRENT_SP0,
> > +
> > +	VECTOR_SYNC_CURRENT,
> > +	VECTOR_IRQ_CURRENT,
> > +	VECTOR_FIQ_CURRENT,
> > +	VECTOR_ERROR_CURRENT,
> > +
> > +	VECTOR_SYNC_LOWER_64,
> > +	VECTOR_IRQ_LOWER_64,
> > +	VECTOR_FIQ_LOWER_64,
> > +	VECTOR_ERROR_LOWER_64,
> > +
> > +	VECTOR_SYNC_LOWER_32,
> > +	VECTOR_IRQ_LOWER_32,
> > +	VECTOR_FIQ_LOWER_32,
> > +	VECTOR_ERROR_LOWER_32,
> > +};
> > +
> > +#define VECTOR_IS_SYNC(v) ((v) == VECTOR_SYNC_CURRENT_SP0 || \
> > +			   (v) == VECTOR_SYNC_CURRENT     || \
> > +			   (v) == VECTOR_SYNC_LOWER_64    || \
> > +			   (v) == VECTOR_SYNC_LOWER_32)
> > +
> > +/* Some common EC (Exception classes) */
> > +#define ESR_EC_ILLEGAL_INS	0x0e
> > +#define ESR_EC_SVC64		0x15
> > +#define ESR_EC_IABORT_CURRENT	0x21
> > +#define ESR_EC_DABORT_CURRENT	0x25
> > +#define ESR_EC_SERROR		0x2f
> > +#define ESR_EC_HW_BP_CURRENT	0x31
> > +#define ESR_EC_SSTEP_CURRENT	0x33
> > +#define ESR_EC_WP_CURRENT	0x35
> > +#define ESR_EC_BRK_INS		0x3C
> > +
> > +#define ESR_EC_NUM		64
> > +
> > +#define ESR_EC_SHIFT		26
> > +#define ESR_EC_MASK		(ESR_EC_NUM - 1)
> > +
> > +void vm_init_descriptor_tables(struct kvm_vm *vm);
> > +void vcpu_init_descriptor_tables(struct kvm_vm *vm, uint32_t vcpuid);
> > +
> > +typedef void(*handler_fn)(struct ex_regs *);
> > +void vm_install_exception_handler(struct kvm_vm *vm,
> > +		int vector, int ec, handler_fn handler);
> > +void vm_install_vector_handler(struct kvm_vm *vm,
> > +		int vector, handler_fn handler);
> > +
> > +#define SPSR_D          (1 << 9)
> > +#define SPSR_SS         (1 << 21)
> > +
> > +#define write_sysreg(reg, val)						  \
> > +({									  \
> > +	u64 __val = (u64)(val);						  \
> > +	asm volatile("msr " __stringify(reg) ", %x0" : : "rZ" (__val));	  \
> > +})
> > +
> > +#define read_sysreg(reg)						  \
> > +({	u64 val;							  \
> > +	asm volatile("mrs %0, "__stringify(reg) : "=r"(val) : : "memory");\
> > +	val;								  \
> > +})
> > +
> >  #endif /* SELFTEST_KVM_PROCESSOR_H */
> > diff --git a/tools/testing/selftests/kvm/lib/aarch64/handlers.S b/tools/testing/selftests/kvm/lib/aarch64/handlers.S
> > new file mode 100644
> > index 000000000000..8a560021892b
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/lib/aarch64/handlers.S
> > @@ -0,0 +1,130 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +.macro save_registers, vector
> > +	add	sp, sp, #-16 * 17
> > +
> > +	stp	x0, x1, [sp, #16 * 0]
> > +	stp	x2, x3, [sp, #16 * 1]
> > +	stp	x4, x5, [sp, #16 * 2]
> > +	stp	x6, x7, [sp, #16 * 3]
> > +	stp	x8, x9, [sp, #16 * 4]
> > +	stp	x10, x11, [sp, #16 * 5]
> > +	stp	x12, x13, [sp, #16 * 6]
> > +	stp	x14, x15, [sp, #16 * 7]
> > +	stp	x16, x17, [sp, #16 * 8]
> > +	stp	x18, x19, [sp, #16 * 9]
> > +	stp	x20, x21, [sp, #16 * 10]
> > +	stp	x22, x23, [sp, #16 * 11]
> > +	stp	x24, x25, [sp, #16 * 12]
> > +	stp	x26, x27, [sp, #16 * 13]
> > +	stp	x28, x29, [sp, #16 * 14]
> > +
> > +	.if \vector >= 8
> > +	mrs	x1, sp_el0
> 
> I'm still a bit perplexed by this. SP_EL0 is never changed, since you
> always run in handler mode. Therefore, saving/restoring it is only
> overhead. If an exception handler wants to introspect it, it is
> already available in the relevant system register.
> 
> Or did you have something else in mind for it?
> 

Not really. The reason for saving sp_el0 in there was just for
consistency, so that handlers for both el0 and el1 exceptions could get
the sp at regs->sp.

Restoring sp_el0 might be too much. So, what do you think of this v3: we
keep the saving of sp_el0 into regs->sp (to keep things the same between
el0 and el1) and delete the restoring of sp_el0?

Thanks,
Ricardo

> > +	.else
> > +	/*
> > +	 * This stores sp_el1 into ex_regs.sp so exception handlers can
> > +	 * "look" at it. It will _not_ be used to restore the sp_el1 on
> > +	 * return from the exception so handlers can not update it.
> > +	 */
> > +	mov	x1, sp
> > +	.endif
> > +	stp	x30, x1, [sp, #16 * 15] /* x30, SP */
> > +
> > +	mrs	x1, elr_el1
> > +	mrs	x2, spsr_el1
> > +	stp	x1, x2, [sp, #16 * 16] /* PC, PSTATE */
> > +.endm
> > +
> > +.macro restore_registers, vector
> > +	ldp	x1, x2, [sp, #16 * 16] /* PC, PSTATE */
> > +	msr	elr_el1, x1
> > +	msr	spsr_el1, x2
> > +
> > +	ldp	x30, x1, [sp, #16 * 15] /* x30, SP */
> > +	.if \vector >= 8
> > +	msr	sp_el0, x1
> > +	.endif
> > +
> > +	ldp	x28, x29, [sp, #16 * 14]
> > +	ldp	x26, x27, [sp, #16 * 13]
> > +	ldp	x24, x25, [sp, #16 * 12]
> > +	ldp	x22, x23, [sp, #16 * 11]
> > +	ldp	x20, x21, [sp, #16 * 10]
> > +	ldp	x18, x19, [sp, #16 * 9]
> > +	ldp	x16, x17, [sp, #16 * 8]
> > +	ldp	x14, x15, [sp, #16 * 7]
> > +	ldp	x12, x13, [sp, #16 * 6]
> > +	ldp	x10, x11, [sp, #16 * 5]
> > +	ldp	x8, x9, [sp, #16 * 4]
> > +	ldp	x6, x7, [sp, #16 * 3]
> > +	ldp	x4, x5, [sp, #16 * 2]
> > +	ldp	x2, x3, [sp, #16 * 1]
> > +	ldp	x0, x1, [sp, #16 * 0]
> > +
> > +	add	sp, sp, #16 * 17
> > +
> > +	eret
> > +.endm
> > +
> > +.pushsection ".entry.text", "ax"
> > +.balign 0x800
> > +.global vectors
> > +vectors:
> > +.popsection
> > +
> > +.set	vector, 0
> > +
> > +/*
> > + * Build an exception handler for vector and append a jump to it into
> > + * vectors (while making sure that it's 0x80 aligned).
> > + */
> > +.macro HANDLER, label
> > +handler_\()\label:
> > +	save_registers vector
> > +	mov	x0, sp
> > +	mov	x1, #vector
> > +	bl	route_exception
> > +	restore_registers vector
> > +
> > +.pushsection ".entry.text", "ax"
> > +.balign 0x80
> > +	b	handler_\()\label
> > +.popsection
> > +
> > +.set	vector, vector + 1
> > +.endm
> > +
> > +.macro HANDLER_INVALID
> > +.pushsection ".entry.text", "ax"
> > +.balign 0x80
> > +/* This will abort so no need to save and restore registers. */
> > +	mov	x0, #vector
> > +	b	kvm_exit_unexpected_vector
> > +.popsection
> > +
> > +.set	vector, vector + 1
> > +.endm
> > +
> > +/*
> > + * Caution: be sure to not add anything between the declaration of vectors
> > + * above and these macro calls that will build the vectors table below it.
> > + */
> > +	HANDLER_INVALID                         // Synchronous EL1t
> > +	HANDLER_INVALID                         // IRQ EL1t
> > +	HANDLER_INVALID                         // FIQ EL1t
> > +	HANDLER_INVALID                         // Error EL1t
> > +
> > +	HANDLER	el1h_sync                       // Synchronous EL1h
> > +	HANDLER	el1h_irq                        // IRQ EL1h
> > +	HANDLER el1h_fiq                        // FIQ EL1h
> > +	HANDLER	el1h_error                      // Error EL1h
> > +
> > +	HANDLER	el0_sync_64                     // Synchronous 64-bit EL0
> > +	HANDLER	el0_irq_64                      // IRQ 64-bit EL0
> > +	HANDLER	el0_fiq_64                      // FIQ 64-bit EL0
> > +	HANDLER	el0_error_64                    // Error 64-bit EL0
> > +
> > +	HANDLER	el0_sync_32                     // Synchronous 32-bit EL0
> > +	HANDLER	el0_irq_32                      // IRQ 32-bit EL0
> > +	HANDLER	el0_fiq_32                      // FIQ 32-bit EL0
> > +	HANDLER	el0_error_32                    // Error 32-bit EL0
> > diff --git a/tools/testing/selftests/kvm/lib/aarch64/processor.c b/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > index cee92d477dc0..25be71ec88be 100644
> > --- a/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > @@ -6,6 +6,7 @@
> >   */
> >  
> >  #include <linux/compiler.h>
> > +#include <assert.h>
> >  
> >  #include "kvm_util.h"
> >  #include "../kvm_util_internal.h"
> > @@ -14,6 +15,8 @@
> >  #define KVM_GUEST_PAGE_TABLE_MIN_PADDR		0x180000
> >  #define DEFAULT_ARM64_GUEST_STACK_VADDR_MIN	0xac0000
> >  
> > +vm_vaddr_t exception_handlers;
> > +
> >  static uint64_t page_align(struct kvm_vm *vm, uint64_t v)
> >  {
> >  	return (v + vm->page_size) & ~(vm->page_size - 1);
> > @@ -334,6 +337,127 @@ void vcpu_args_set(struct kvm_vm *vm, uint32_t vcpuid, unsigned int num, ...)
> >  	va_end(ap);
> >  }
> >  
> > +void kvm_exit_unexpected_vector(int vector)
> > +{
> > +	ucall(UCALL_UNHANDLED, 3, vector, 0, false /* !valid_ec */);
> > +}
> > +
> > +void kvm_exit_unexpected_exception(int vector, uint64_t ec)
> > +{
> > +	ucall(UCALL_UNHANDLED, 3, vector, ec, true /* valid_ec */);
> > +}
> > +
> >  void assert_on_unhandled_exception(struct kvm_vm *vm, uint32_t vcpuid)
> >  {
> > +	struct ucall uc;
> > +
> > +	if (get_ucall(vm, vcpuid, &uc) != UCALL_UNHANDLED)
> > +		return;
> > +
> > +	if (uc.args[2]) /* valid_ec */ {
> > +		assert(VECTOR_IS_SYNC(uc.args[0]));
> > +		TEST_ASSERT(false,
> > +			"Unexpected exception (vector:0x%lx, ec:0x%lx)",
> > +			uc.args[0], uc.args[1]);
> > +	} else {
> > +		assert(!VECTOR_IS_SYNC(uc.args[0]));
> > +		TEST_ASSERT(false,
> > +			"Unexpected exception (vector:0x%lx)",
> > +			uc.args[0]);
> > +	}
> > +}
> > +
> > +/*
> > + * This exception handling code was heavily inspired on kvm-unit-tests. There
> > + * is a set of default vector handlers stored in vector_handlers. These default
> > + * vector handlers call user-installed handlers stored in exception_handlers.
> > + * Synchronous handlers are indexed by (vector, ec), and irq handlers by
> > + * (vector, ec=0).
> > + */
> > +
> > +typedef void(*vector_fn)(struct ex_regs *, int vector);
> > +
> > +struct handlers {
> > +	vector_fn vector_handlers[VECTOR_NUM];
> > +	handler_fn exception_handlers[VECTOR_NUM][ESR_EC_NUM];
> > +};
> > +
> > +void vcpu_init_descriptor_tables(struct kvm_vm *vm, uint32_t vcpuid)
> > +{
> > +	extern char vectors;
> > +
> > +	set_reg(vm, vcpuid, ARM64_SYS_REG(VBAR_EL1), (uint64_t)&vectors);
> > +}
> > +
> > +void default_sync_handler(struct ex_regs *regs, int vector)
> > +{
> > +	struct handlers *handlers = (struct handlers *)exception_handlers;
> > +	uint64_t esr = read_sysreg(esr_el1);
> > +	uint64_t ec = (esr >> ESR_EC_SHIFT) & ESR_EC_MASK;
> > +
> > +	GUEST_ASSERT(VECTOR_IS_SYNC(vector));
> > +
> > +	if (handlers && handlers->exception_handlers[vector][ec])
> > +		handlers->exception_handlers[vector][ec](regs);
> > +	else
> > +		kvm_exit_unexpected_exception(vector, ec);
> > +}
> > +
> > +void default_irq_handler(struct ex_regs *regs, int vector)
> > +{
> > +	struct handlers *handlers = (struct handlers *)exception_handlers;
> > +
> > +	GUEST_ASSERT(!VECTOR_IS_SYNC(vector));
> > +
> > +	if (handlers && handlers->exception_handlers[vector][0])
> > +		handlers->exception_handlers[vector][0](regs);
> > +	else
> > +		kvm_exit_unexpected_vector(vector);
> > +}
> > +
> > +void route_exception(struct ex_regs *regs, int vector)
> > +{
> > +	struct handlers *handlers = (struct handlers *)exception_handlers;
> > +
> > +	if (handlers && handlers->vector_handlers[vector])
> > +		handlers->vector_handlers[vector](regs, vector);
> > +	else
> > +		kvm_exit_unexpected_vector(vector);
> > +}
> > +
> > +void vm_init_descriptor_tables(struct kvm_vm *vm)
> > +{
> > +	struct handlers *handlers;
> > +
> > +	vm->handlers = vm_vaddr_alloc(vm, sizeof(struct handlers),
> > +			vm->page_size, 0, 0);
> > +
> > +	handlers = (struct handlers *)addr_gva2hva(vm, vm->handlers);
> > +	handlers->vector_handlers[VECTOR_SYNC_CURRENT] = default_sync_handler;
> > +	handlers->vector_handlers[VECTOR_IRQ_CURRENT] = default_irq_handler;
> > +	handlers->vector_handlers[VECTOR_SYNC_LOWER_64] = default_sync_handler;
> > +	handlers->vector_handlers[VECTOR_IRQ_LOWER_64] = default_irq_handler;
> 
> How about FIQ, Error? Although they are unlikely, they are valid
> exceptions.
> 
> > +
> > +	*(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
> > +}
> > +
> > +void vm_install_exception_handler(struct kvm_vm *vm, int vector, int ec,
> > +			 void (*handler)(struct ex_regs *))
> > +{
> > +	struct handlers *handlers = (struct handlers *)addr_gva2hva(vm, vm->handlers);
> > +
> > +	assert(VECTOR_IS_SYNC(vector));
> > +	assert(vector < VECTOR_NUM);
> > +	assert(ec < ESR_EC_NUM);
> > +	handlers->exception_handlers[vector][ec] = handler;
> > +}
> > +
> > +void vm_install_vector_handler(struct kvm_vm *vm, int vector,
> > +			 void (*handler)(struct ex_regs *))
> > +{
> > +	struct handlers *handlers = (struct handlers *)addr_gva2hva(vm, vm->handlers);
> > +
> > +	assert(!VECTOR_IS_SYNC(vector));
> > +	assert(vector < VECTOR_NUM);
> > +	handlers->exception_handlers[vector][0] = handler;
> >  }
> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.