From: Jack Thomson <[email protected]> Don't return -EAGAIN from stage2_map_walker_try_leaf during KVM_PRE_FAULT_MEMORY.
During pre-faults, user_abort() is retried upon returning -EAGAIN, meaning the ioctl would get stuck in an infinite loop if userspace tries to pre-fault already existing mappings Signed-off-by: Jack Thomson <[email protected]> --- arch/arm64/include/asm/kvm_pgtable.h | 3 +++ arch/arm64/kvm/hyp/pgtable.c | 6 +++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h index 2888b5d03757..0789671d1c4f 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h @@ -296,6 +296,8 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end, * @KVM_PGTABLE_WALK_SKIP_CMO: Visit and update table entries * without Cache maintenance * operations required. + * @KVM_PGTABLE_WALK_PRE_FAULT Indicates the page-table walk was + * invoked from a pre-fault request. */ enum kvm_pgtable_walk_flags { KVM_PGTABLE_WALK_LEAF = BIT(0), @@ -305,6 +307,7 @@ enum kvm_pgtable_walk_flags { KVM_PGTABLE_WALK_HANDLE_FAULT = BIT(4), KVM_PGTABLE_WALK_SKIP_BBM_TLBI = BIT(5), KVM_PGTABLE_WALK_SKIP_CMO = BIT(6), + KVM_PGTABLE_WALK_PRE_FAULT = BIT(7), }; struct kvm_pgtable_visit_ctx { diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index c351b4abd5db..140dccec2c5b 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -914,9 +914,13 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx, * same mapping or only change the access permissions. Instead, * the vCPU will exit one more time from guest if still needed * and then go through the path of relaxing permissions. + * + * When walking in the context of a pre-fault request, if the + * mapping already exists we can return 0, as there's nothing + * to do. */ if (!stage2_pte_needs_update(ctx->old, new)) - return -EAGAIN; + return (ctx->flags & KVM_PGTABLE_WALK_PRE_FAULT) ? 0 : -EAGAIN; /* If we're only changing software bits, then store them and go! */ if (!kvm_pgtable_walk_shared(ctx) && -- 2.43.0
