From: Fuad Tabba Date: Fri, 1 May 2026 11:21:49 +0000 (+0100) Subject: KVM: arm64: Pre-check vcpu memcache for host->guest donate X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=effc0a39b8e0f30670fe24f51e44329d4324e566;p=thirdparty%2Flinux.git KVM: arm64: Pre-check vcpu memcache for host->guest donate __pkvm_host_donate_guest() flips the host stage-2 PTE for the donated page to a non-valid annotation via host_stage2_set_owner_metadata_locked() and then calls kvm_pgtable_stage2_map() to install the matching guest stage-2 mapping. The map's return value is wrapped in WARN_ON() and otherwise discarded, asserting that the call cannot fail. WARN_ON() at nVHE EL2 panics, so this assertion is only correct if the call genuinely cannot fail. kvm_pgtable_stage2_map() can fail with -ENOMEM even at PAGE_SIZE granularity: the donate path verifies PKVM_NOPAGE for the guest IPA before the map, so the walker must allocate fresh page-table pages from the vcpu memcache, and the host controls the vcpu memcache via the topup interface. An under-provisioned donation request would otherwise turn a recoverable -ENOMEM into a fatal hyp panic. Bound the worst-case walker allocation alongside the existing __host_check_page_state_range() / __guest_check_page_state_range() pre-checks, using the helper introduced for host->guest share. If the vcpu memcache holds fewer pages than kvm_mmu_cache_min_pages(), return -ENOMEM before any state mutation. Fixes: 1e579adca177 ("KVM: arm64: Introduce __pkvm_host_donate_guest()") Assisted-by: Gemini:gemini-3.1-pro review-prompts Signed-off-by: Fuad Tabba Link: https://patch.msgid.link/20260501112149.2824881-7-tabba@google.com Signed-off-by: Marc Zyngier --- diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c index ffb123fc1145..25f04629014e 100644 --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c @@ -1425,6 +1425,10 @@ int __pkvm_host_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu) if (ret) goto unlock; + ret = __guest_check_pgtable_memcache(vcpu); + if (ret) + goto unlock; + meta = host_stage2_encode_gfn_meta(vm, gfn); WARN_ON(host_stage2_set_owner_metadata_locked(phys, PAGE_SIZE, PKVM_ID_GUEST, meta));