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

[Auger Eric <eric.auger@redhat.com>]

Hi Ricardo,

On 5/3/21 9:12 PM, Ricardo Koller wrote:
> 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.

running the test on 5.12 I get

==== Test Assertion Failure ====
  aarch64/debug-exceptions.c:232: false
  pid=6477 tid=6477 errno=4 - Interrupted system call
     1	0x000000000040147b: main at debug-exceptions.c:230
     2	0x000003ff8aa60de3: ?? ??:0
     3	0x0000000000401517: _start at :?
  Failed guest assert: hw_bp_addr == PC(hw_bp) at
aarch64/debug-exceptions.c:105
	values: 0, 0x401794


I guess it is not an expected result. Any known bug waiting on the list?


Thanks

Eric

>>>
>>> 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.
>