Re: [PATCH 2/2] KVM: LoongArch: selftests: Add in-kernel MMIO read fast path test

On 2026/7/23 下午7:16, Zeng Chi wrote:
> From: Zeng Chi <[email protected]>
> 
> Add a test that exercises the in-kernel MMIO read fast path of
> kvm_emu_mmio_read(). The guest performs an MMIO read from an in-kernel
> emulated PCH-PIC, immediately followed by a marker instruction, and the
> test verifies that the marker instruction is executed, i.e. that the PC
> advances by exactly one instruction instead of skipping the instruction
> after the MMIO read.
> 
> The test skips gracefully when the host KVM cannot create a PCH-PIC
> device.
> 
> Signed-off-by: Zeng Chi <[email protected]>
> ---
>   tools/testing/selftests/kvm/Makefile.kvm      |  3 +-
>   .../selftests/kvm/loongarch/mmio_read_test.c  | 89 +++++++++++++++++++
>   2 files changed, 91 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/kvm/loongarch/mmio_read_test.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index 6fc34e9bf8e1..4daf90caaabc 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -228,7 +228,8 @@ TEST_GEN_PROGS_riscv += mmu_stress_test
>   TEST_GEN_PROGS_riscv += rseq_test
>   TEST_GEN_PROGS_riscv += steal_time
>   
> -TEST_GEN_PROGS_loongarch = loongarch/pmu_test
> +TEST_GEN_PROGS_loongarch = loongarch/mmio_read_test
> +TEST_GEN_PROGS_loongarch += loongarch/pmu_test
>   TEST_GEN_PROGS_loongarch += arch_timer
>   TEST_GEN_PROGS_loongarch += coalesced_io_test
>   TEST_GEN_PROGS_loongarch += demand_paging_test
> diff --git a/tools/testing/selftests/kvm/loongarch/mmio_read_test.c b/tools/testing/selftests/kvm/loongarch/mmio_read_test.c
> new file mode 100644
> index 000000000000..7f64ca91ca8f
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/loongarch/mmio_read_test.c
> @@ -0,0 +1,89 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * LoongArch KVM in-kernel MMIO read fast path test
> + *
> + * When an MMIO read hits a device emulated inside KVM (such as the
> + * PCH-PIC), kvm_emu_mmio_read() completes the access without returning
> + * to user space and advances the guest PC by one instruction.
> + *
> + * This test issues such an in-kernel MMIO read immediately followed by
> + * a marker instruction and checks that the marker instruction actually
> + * runs, i.e. that the PC advanced by exactly one instruction (4 bytes)
> + * rather than skipping the instruction after the MMIO read.
> + */
> +#include "kvm_util.h"
> +#include "processor.h"
> +#include "test_util.h"
> +#include "loongarch/processor.h"
> +
> +/* Physical base the in-kernel PCH-PIC is mapped at (no memslot backs it) */
> +#define PCH_PIC_BASE		0x10000000UL
> +
> +static void guest_code(void)
> +{
> +	unsigned long marker = 0;
> +	unsigned int val = 0;
> +
> +	/*
> +	 * 'ld.w' faults out as an MMIO read and is emulated in kernel.
> +	 * The following 'addi.d' must execute; it is skipped if the MMIO
> +	 * read fast path advances the PC twice (by 8 instead of 4).
> +	 */
> +	asm volatile(
> +		"ld.w	%[val], %[base], 0\n\t"
> +		"addi.d	%[marker], %[marker], 1\n\t"
> +		: [val] "=&r" (val), [marker] "+&r" (marker)
> +		: [base] "r" (PCH_PIC_BASE)
> +		: "memory");
By my understanding, the kvm selftest is mainly to test function. It 
will be better if it is to verify irq handling with in-kernel PCH-PIC 
irqchip.

Regards
Bibo Mao
> +
> +	GUEST_PRINTF("mmio read val=0x%x, marker=%lu\n", val, marker);
> +	GUEST_ASSERT_EQ(marker, 1);
> +	GUEST_DONE();
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	struct ucall uc;
> +	uint64_t addr = PCH_PIC_BASE;
> +	int dev_fd;
> +
> +	vm = vm_create(VM_MODE_P47V47_16K);
> +	vcpu = vm_vcpu_add(vm, 0, guest_code);
> +
> +	/* Create the in-kernel PCH-PIC and map it at PCH_PIC_BASE */
> +	dev_fd = __kvm_create_device(vm, KVM_DEV_TYPE_LOONGARCH_PCHPIC);
> +	if (dev_fd < 0) {
> +		print_skip("PCH-PIC device not supported by host KVM");
> +		kvm_vm_free(vm);
> +		return KSFT_SKIP;
> +	}
> +	kvm_device_attr_set(dev_fd, KVM_DEV_LOONGARCH_PCH_PIC_GRP_CTRL,
> +			    KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT, &addr);
> +	close(dev_fd);
> +
> +	/* Identity-map the MMIO page so the guest can reach the device */
> +	virt_map(vm, PCH_PIC_BASE, PCH_PIC_BASE, 1);
> +
> +	while (1) {
> +		vcpu_run(vcpu);
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_PRINTF:
> +			pr_info("%s", uc.buffer);
> +			break;
> +		case UCALL_DONE:
> +			goto done;
> +		case UCALL_ABORT:
> +			REPORT_GUEST_ASSERT(uc);
> +			goto done;
> +		default:
> +			TEST_FAIL("Unexpected exit: %s",
> +				  exit_reason_str(vcpu->run->exit_reason));
> +		}
> +	}
> +
> +done:
> +	kvm_vm_free(vm);
> +	return 0;
> +}
>