Commit 03db5f05 authored by Zenghui Yu (Huawei)'s avatar Zenghui Yu (Huawei) Committed by Marc Zyngier
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KVM: arm64: selftests: Avoid testing the IMPDEF behavior 

It turned out that we can't really force KVM to use the "slow" path when
emulating AT instructions [1]. We should therefore avoid testing the IMPDEF
behavior (i.e., TEST_ACCESS_FLAG - address translation instructions are
permitted to update AF but not required).

Remove it and improve the comment a bit.

[1] https://lore.kernel.org/r/b951dcfb-0ad1-4d7b-b6ce-d54b272dd9be@linux.dev



Signed-off-by: default avatarZenghui Yu (Huawei) <zenghui.yu@linux.dev>
Link: https://patch.msgid.link/20260317131558.52751-1-zenghui.yu@linux.dev


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent a3ca3bfd

tools/testing/selftests/kvm/arm64/at.c

+2 −12
Original line number Diff line number Diff line
@@ -13,7 +13,6 @@ 


enum {

	CLEAR_ACCESS_FLAG,

	TEST_ACCESS_FLAG,

};



static u64 *ptep_hva;
@@ -49,7 +48,6 @@ do { \ 
		GUEST_ASSERT_EQ(FIELD_GET(SYS_PAR_EL1_ATTR, par), MAIR_ATTR_NORMAL);	\

		GUEST_ASSERT_EQ(FIELD_GET(SYS_PAR_EL1_SH, par), PTE_SHARED >> 8);	\

		GUEST_ASSERT_EQ(par & SYS_PAR_EL1_PA, TEST_ADDR);			\

		GUEST_SYNC(TEST_ACCESS_FLAG);						\

	}										\

} while (0)
@@ -85,10 +83,6 @@ static void guest_code(void) 
	if (!SYS_FIELD_GET(ID_AA64MMFR1_EL1, HAFDBS, read_sysreg(id_aa64mmfr1_el1)))

		GUEST_DONE();



	/*

	 * KVM's software PTW makes the implementation choice that the AT

	 * instruction sets the access flag.

	 */

	sysreg_clear_set(tcr_el1, 0, TCR_HA);

	isb();

	test_at(false);
@@ -102,8 +96,8 @@ static void handle_sync(struct kvm_vcpu *vcpu, struct ucall *uc) 
	case CLEAR_ACCESS_FLAG:

		/*

		 * Delete + reinstall the memslot to invalidate stage-2

		 * mappings of the stage-1 page tables, forcing KVM to

		 * use the 'slow' AT emulation path.

		 * mappings of the stage-1 page tables, allowing KVM to

		 * potentially use the 'slow' AT emulation path.

		 *

		 * This and clearing the access flag from host userspace

		 * ensures that the access flag cannot be set speculatively
@@ -112,10 +106,6 @@ static void handle_sync(struct kvm_vcpu *vcpu, struct ucall *uc) 
		clear_bit(__ffs(PTE_AF), ptep_hva);

		vm_mem_region_reload(vcpu->vm, vcpu->vm->memslots[MEM_REGION_PT]);

		break;

	case TEST_ACCESS_FLAG:

		TEST_ASSERT(test_bit(__ffs(PTE_AF), ptep_hva),

			    "Expected access flag to be set (desc: %lu)", *ptep_hva);

		break;

	default:

		TEST_FAIL("Unexpected SYNC arg: %lu", uc->args[1]);

	}