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KVM: arm64: selftests: Cope with arch silliness in EL2 selftest

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Implementations without FEAT_FGT aren't required to trap the entire ID
register space when HCR_EL2.TID3 is set. This is a terrible idea, as the
hypervisor may need to advertise the absence of a feature to the VM
using a negative value in a signed field, FEAT_E2H0 being a great
example of this.

Cope with uncooperative implementations in the EL2 selftest by accepting
a zero value when FEAT_FGT is absent and otherwise only tolerating the
expected nonzero value.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Oliver Upton 2025-09-23 10:30:06 -07:00 committed by Marc Zyngier
parent f677b0efa9
commit 75b2fdc1a8
1 changed files with 15 additions and 2 deletions
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17
tools/testing/selftests/kvm/arm64/hello_el2.c
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@ -13,15 +13,28 @@
static void guest_code(void)
{
u64 mmfr0 = read_sysreg_s(SYS_ID_AA64MMFR0_EL1);
u64 mmfr1 = read_sysreg_s(SYS_ID_AA64MMFR1_EL1);
u64 mmfr4 = read_sysreg_s(SYS_ID_AA64MMFR4_EL1);
u8 e2h0 = SYS_FIELD_GET(ID_AA64MMFR4_EL1, E2H0, mmfr4);
GUEST_ASSERT_EQ(get_current_el(), 2);
GUEST_ASSERT(read_sysreg(hcr_el2) & HCR_EL2_E2H);
GUEST_ASSERT_EQ(SYS_FIELD_GET(ID_AA64MMFR1_EL1, VH, mmfr1),
ID_AA64MMFR1_EL1_VH_IMP);
GUEST_ASSERT_EQ(SYS_FIELD_GET(ID_AA64MMFR4_EL1, E2H0, mmfr4),
ID_AA64MMFR4_EL1_E2H0_NI_NV1);
/*
* Traps of the complete ID register space are IMPDEF without FEAT_FGT,
* which is really annoying to deal with in KVM describing E2H as RES1.
*
* If the implementation doesn't honor the trap then expect the register
* to return all zeros.
*/
if (e2h0 == ID_AA64MMFR4_EL1_E2H0_IMP)
GUEST_ASSERT_EQ(SYS_FIELD_GET(ID_AA64MMFR0_EL1, FGT, mmfr0),
ID_AA64MMFR0_EL1_FGT_NI);
else
GUEST_ASSERT_EQ(e2h0, ID_AA64MMFR4_EL1_E2H0_NI_NV1);
GUEST_DONE();
}