[PATCH 1/2] KVM: arm64: fix config.hcr used uninitialized in __kvm_at_s1e01_fast

D Scott Phillips
2025-04-15T15:47:05Z

In the skip_mmu_switch case, config.hcr was used uninitialized. On my
machine that caused garbage to be written to HCR_EL2 and then the CPU
got stuck at the synchronous exception handler. Also, the restore of
HCR_EL2 was missing at the end of the function in the same case.

In skip_mmu_switch case, initialize config.hcr with HCR_HOST_VHE_FLAGS.

Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
---
arch/arm64/kvm/at.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index f74a66ce3064b..ff4b06ce661af 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -1233,8 +1233,10 @@ static u64 __kvm_at_s1e01_fast(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
* the right one (as we trapped from vEL2). If not, save the
* full MMU context.
*/
- if (vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu))
+ if (vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu)) {
+ config.hcr = read_sysreg(hcr_el2);
goto skip_mmu_switch;
+ }

/*
* Obtaining the S2 MMU for a L2 is horribly racy, and we may not
@@ -1299,7 +1301,9 @@ static u64 __kvm_at_s1e01_fast(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
if (!fail)
par = read_sysreg_par();

- if (!(vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu)))
+ if (vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu))
+ write_sysreg(config.hcr, hcr_el2);
+ else
__mmu_config_restore(&config);

return par;
--
2.48.1