Commit b9635930 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: selftests: Provide error code as a KVM_ASM_SAFE() output 



Provide the error code on a fault in KVM_ASM_SAFE(), e.g. to allow tests
to assert that #PF generates the correct error code without needing to
manually install a #PF handler.  Use r10 as the scratch register for the
error code, as it's already clobbered by the asm blob (loaded with the
RIP of the to-be-executed instruction).  Deliberately load the output
"error_code" even in the non-faulting path so that error_code is always
initialized with deterministic data (the aforementioned RIP), i.e to
ensure a selftest won't end up with uninitialized consumption regardless
of how KVM_ASM_SAFE() is used.

Don't clear r10 in the non-faulting case and instead load error code with
the RIP (see above).  The error code is valid if and only if an exception
occurs, and '0' isn't necessarily a better "invalid" value, e.g. '0'
could result in false passes for a buggy test.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20221102184654.282799-9-dmatlack@google.com
parent f2e5b53b

tools/testing/selftests/kvm/include/x86_64/processor.h

+27 −12
Original line number Diff line number Diff line
@@ -786,6 +786,7 @@ void vm_install_exception_handler(struct kvm_vm *vm, int vector, 
 *

 * REGISTER OUTPUTS:

 * r9  = exception vector (non-zero)

 * r10 = error code

 */

#define KVM_ASM_SAFE(insn)					\

	"mov $" __stringify(KVM_EXCEPTION_MAGIC) ", %%r9\n\t"	\
@@ -794,17 +795,30 @@ void vm_install_exception_handler(struct kvm_vm *vm, int vector, 
	"1: " insn "\n\t"					\

	"xor %%r9, %%r9\n\t"					\

	"2:\n\t"						\

	"mov  %%r9b, %[vector]\n\t"

	"mov  %%r9b, %[vector]\n\t"				\

	"mov  %%r10, %[error_code]\n\t"



#define KVM_ASM_SAFE_OUTPUTS(v)	[vector] "=qm"(v)

#define KVM_ASM_SAFE_OUTPUTS(v, ec)	[vector] "=qm"(v), [error_code] "=rm"(ec)

#define KVM_ASM_SAFE_CLOBBERS	"r9", "r10", "r11"



#define kvm_asm_safe(insn, inputs...)					\

({									\

	uint64_t ign_error_code;					\

	uint8_t vector;							\

									\

	asm volatile(KVM_ASM_SAFE(insn)					\

		     : KVM_ASM_SAFE_OUTPUTS(vector)	\

		     : KVM_ASM_SAFE_OUTPUTS(vector, ign_error_code)	\

		     : inputs						\

		     : KVM_ASM_SAFE_CLOBBERS);				\

	vector;								\

})



#define kvm_asm_safe_ec(insn, error_code, inputs...)			\

({									\

	uint8_t vector;							\

									\

	asm volatile(KVM_ASM_SAFE(insn)					\

		     : KVM_ASM_SAFE_OUTPUTS(vector, error_code)		\

		     : inputs						\

		     : KVM_ASM_SAFE_CLOBBERS);				\

	vector;								\
@@ -812,11 +826,12 @@ void vm_install_exception_handler(struct kvm_vm *vm, int vector, 


static inline uint8_t rdmsr_safe(uint32_t msr, uint64_t *val)

{

	uint64_t error_code;

	uint8_t vector;

	uint32_t a, d;



	asm volatile(KVM_ASM_SAFE("rdmsr")

		     : "=a"(a), "=d"(d), KVM_ASM_SAFE_OUTPUTS(vector)

		     : "=a"(a), "=d"(d), KVM_ASM_SAFE_OUTPUTS(vector, error_code)

		     : "c"(msr)

		     : KVM_ASM_SAFE_CLOBBERS);

tools/testing/selftests/kvm/lib/x86_64/processor.c

+1 −0
Original line number Diff line number Diff line
@@ -1068,6 +1068,7 @@ static bool kvm_fixup_exception(struct ex_regs *regs) 


	regs->rip = regs->r11;

	regs->r9 = regs->vector;

	regs->r10 = regs->error_code;

	return true;

}

tools/testing/selftests/kvm/x86_64/hyperv_features.c

+2 −1
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
static inline uint8_t hypercall(u64 control, vm_vaddr_t input_address,

				vm_vaddr_t output_address, uint64_t *hv_status)

{

	uint64_t error_code;

	uint8_t vector;



	/* Note both the hypercall and the "asm safe" clobber r9-r11. */
@@ -25,7 +26,7 @@ static inline uint8_t hypercall(u64 control, vm_vaddr_t input_address, 
		     KVM_ASM_SAFE("vmcall")

		     : "=a" (*hv_status),

		       "+c" (control), "+d" (input_address),

		       KVM_ASM_SAFE_OUTPUTS(vector)

		       KVM_ASM_SAFE_OUTPUTS(vector, error_code)

		     : [output_address] "r"(output_address),

		       "a" (-EFAULT)

		     : "cc", "memory", "r8", KVM_ASM_SAFE_CLOBBERS);