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[34.77.69.137]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-475641e4542sm18270184f8f.10.2026.07.01.06.31.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2026 06:31:52 -0700 (PDT) Date: Wed, 1 Jul 2026 14:31:49 +0100 From: Vincent Donnefort To: Bradley Morgan Cc: Marc Zyngier , Oliver Upton , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Quentin Perret , Gavin Shan , Alexandru Elisei , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/3] KVM: arm64: skip pKVM cache flushes for non cacheable mappings Message-ID: References: <20260624160028.15591-1-include@grrlz.net> <20260624160028.15591-2-include@grrlz.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260624160028.15591-2-include@grrlz.net> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260701_063157_862803_02177784 X-CRM114-Status: GOOD ( 26.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jun 24, 2026 at 04:00:26PM +0000, Bradley Morgan wrote: > pKVM keeps its own mapping list for stage 2 operations. Its flush path > uses that list directly, so it lost the PTE attribute check done by the > generic stage 2 walker. > > Record whether a mapping is cacheable and skip cache maintenance for > mappings that are not cacheable. > > Fixes: e912efed485a ("KVM: arm64: Introduce the EL1 pKVM MMU") > Signed-off-by: Bradley Morgan > --- > arch/arm64/kvm/pkvm.c | 51 ++++++++++++++++++++++++++++++++++--------- > 1 file changed, 41 insertions(+), 10 deletions(-) > > diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c > index 428723b1b0f5..ca6e823028c2 100644 > --- a/arch/arm64/kvm/pkvm.c > +++ b/arch/arm64/kvm/pkvm.c > @@ -302,9 +302,32 @@ static u64 __pkvm_mapping_start(struct pkvm_mapping *m) > return m->gfn * PAGE_SIZE; > } > > +#define PKVM_MAPPING_NR_PAGES_MASK GENMASK_ULL(47, 0) > +#define PKVM_MAPPING_CACHEABLE BIT_ULL(48) Probably better to make it "_NC". Protected VMs only support cacheable and they also use struct pkvm_mapping. > + > +static u64 pkvm_mapping_nr_pages(struct pkvm_mapping *m) > +{ > + return m->nr_pages & PKVM_MAPPING_NR_PAGES_MASK; > +} > + > +static bool pkvm_mapping_is_cacheable(struct pkvm_mapping *m) > +{ > + return m->nr_pages & PKVM_MAPPING_CACHEABLE; > +} > + > +static void pkvm_mapping_set_nr_pages(struct pkvm_mapping *m, u64 nr_pages, > + bool cacheable) > +{ > + WARN_ON_ONCE(nr_pages & ~PKVM_MAPPING_NR_PAGES_MASK); > + > + m->nr_pages = nr_pages & PKVM_MAPPING_NR_PAGES_MASK; > + if (cacheable) > + m->nr_pages |= PKVM_MAPPING_CACHEABLE; > +} > + > static u64 __pkvm_mapping_end(struct pkvm_mapping *m) > { > - return (m->gfn + m->nr_pages) * PAGE_SIZE - 1; > + return (m->gfn + pkvm_mapping_nr_pages(m)) * PAGE_SIZE - 1; > } Perhaps using a bitfield would heavily simplify this code? struct pkvm_mapping { ... u64 nr_pages : 63 u64 flags : 1 } Or alternatively, could just make nr_pages u32 and flags u32. nr_pages will not exceed PMD_SIZE / PAGE_SIZE, which is at worst 8192 on 64K systems. > > INTERVAL_TREE_DEFINE(struct pkvm_mapping, node, u64, __subtree_last, > @@ -350,7 +373,7 @@ static int __pkvm_pgtable_stage2_reclaim(struct kvm_pgtable *pgt, u64 start, u64 > continue; > > page = pfn_to_page(mapping->pfn); > - WARN_ON_ONCE(mapping->nr_pages != 1); > + WARN_ON_ONCE(pkvm_mapping_nr_pages(mapping) != 1); > unpin_user_pages_dirty_lock(&page, 1, true); > account_locked_vm(kvm->mm, 1, false); > pkvm_mapping_remove(mapping, &pgt->pkvm_mappings); > @@ -369,7 +392,7 @@ static int __pkvm_pgtable_stage2_unshare(struct kvm_pgtable *pgt, u64 start, u64 > > for_each_mapping_in_range_safe(pgt, start, end, mapping) { > ret = kvm_call_hyp_nvhe(__pkvm_host_unshare_guest, handle, mapping->gfn, > - mapping->nr_pages); > + pkvm_mapping_nr_pages(mapping)); > if (WARN_ON(ret)) > return ret; > pkvm_mapping_remove(mapping, &pgt->pkvm_mappings); > @@ -448,7 +471,7 @@ int pkvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, > * permission faults are handled in the relax_perms() path. > */ > if (mapping) { > - if (size == (mapping->nr_pages * PAGE_SIZE)) > + if (size == (pkvm_mapping_nr_pages(mapping) * PAGE_SIZE)) > return -EAGAIN; > > /* > @@ -472,7 +495,9 @@ int pkvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, > swap(mapping, cache->mapping); > mapping->gfn = gfn; > mapping->pfn = pfn; > - mapping->nr_pages = size / PAGE_SIZE; > + pkvm_mapping_set_nr_pages(mapping, size / PAGE_SIZE, > + !(prot & (KVM_PGTABLE_PROT_DEVICE | > + KVM_PGTABLE_PROT_NORMAL_NC))); > pkvm_mapping_insert(mapping, &pgt->pkvm_mappings); > > return ret; > @@ -503,7 +528,7 @@ int pkvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size) > lockdep_assert_held(&kvm->mmu_lock); > for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) { > ret = kvm_call_hyp_nvhe(__pkvm_host_wrprotect_guest, handle, mapping->gfn, > - mapping->nr_pages); > + pkvm_mapping_nr_pages(mapping)); > if (WARN_ON(ret)) > break; > } > @@ -517,9 +542,13 @@ int pkvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size) > struct pkvm_mapping *mapping; > > lockdep_assert_held(&kvm->mmu_lock); > - for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) > + for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) { > + if (!pkvm_mapping_is_cacheable(mapping)) > + continue; > + > __clean_dcache_guest_page(pfn_to_kaddr(mapping->pfn), > - PAGE_SIZE * mapping->nr_pages); > + PAGE_SIZE * pkvm_mapping_nr_pages(mapping)); > + } > > return 0; > } > @@ -536,8 +565,10 @@ bool pkvm_pgtable_stage2_test_clear_young(struct kvm_pgtable *pgt, u64 addr, u64 > > lockdep_assert_held(&kvm->mmu_lock); > for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) > - young |= kvm_call_hyp_nvhe(__pkvm_host_test_clear_young_guest, handle, mapping->gfn, > - mapping->nr_pages, mkold); > + young |= kvm_call_hyp_nvhe(__pkvm_host_test_clear_young_guest, > + handle, mapping->gfn, > + pkvm_mapping_nr_pages(mapping), > + mkold); > > return young; > } > -- > 2.53.0 >