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[34.34.182.0]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b2a555e59dsm69647405e9.0.2026.11.03.06.52.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 06:52:40 -0800 (PST) Date: Tue, 3 Nov 2026 14:52:36 +0000 From: Vincent Donnefort To: Fuad Tabba Cc: Marc Zyngier , Oliver Upton , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Raghavendra Rao Ananta , Fuad Tabba Subject: Re: [PATCH 1/3] KVM: arm64: Don't walk the whole IPA space when destroying a pKVM stage-2 Message-ID: References: <20261103084742.1302597-1-fuad.tabba@linux.dev> <20261103084742.1302597-2-fuad.tabba@linux.dev> X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103084742.1302597-2-fuad.tabba@linux.dev> On Tue, Nov 03, 2026 at 08:47:40AM +0000, Fuad Tabba wrote: > Since commit 4ddfab5436b6 ("KVM: arm64: Reschedule as needed when > destroying the stage-2 page-tables"), kvm_stage2_destroy() steps through > the IPA space in block-sized chunks, and with pKVM each chunk is a > lookup in the VM's mapping tree. However, pKVM gives every VM the host's > IPA limit, so with LPA2 a teardown makes 2^27 lookups with 16K pages > (2^22 with 4K), nearly all of them for empty space. > > Walk the mapping tree once instead, and reschedule after passing each > mapping to the reclaim or unshare helper. The unshare helper can't > reschedule itself, as the map and unmap paths call it under the > mmu_lock. A failed unshare now leaves only its own mapping behind, not > the rest of its chunk. Not a problem now, but don't we make the device assignment story harder? > > Fixes: 4ddfab5436b69 ("KVM: arm64: Reschedule as needed when destroying the stage-2 page-tables") Isn't it an optimisation? > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/mmu.c | 7 ++++++- > arch/arm64/kvm/pkvm.c | 17 +++++++++++++---- > 2 files changed, 19 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 1db10d8d6db73..42977cf8a7f5d 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1022,7 +1022,12 @@ static void kvm_stage2_destroy(struct kvm_pgtable *pgt) > { > unsigned int ia_bits = VTCR_EL2_IPA(pgt->mmu->vtcr); > > - stage2_destroy_range(pgt, 0, BIT(ia_bits)); > + /* pKVM walks its mapping tree, not the IPA space, and reschedules per mapping */ > + if (is_protected_kvm_enabled()) > + pkvm_pgtable_stage2_destroy_range(pgt, 0, BIT(ia_bits)); > + else > + stage2_destroy_range(pgt, 0, BIT(ia_bits)); > + > KVM_PGT_FN(kvm_pgtable_stage2_destroy_pgd)(pgt); > } > > diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c > index 016997288fd23..992ed3ca6bdd9 100644 > --- a/arch/arm64/kvm/pkvm.c > +++ b/arch/arm64/kvm/pkvm.c > @@ -504,6 +504,7 @@ void pkvm_pgtable_stage2_destroy_range(struct kvm_pgtable *pgt, > { > struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu); > pkvm_handle_t handle = kvm->arch.pkvm.handle; > + struct pkvm_mapping *mapping; > > if (!handle) > return; > @@ -513,10 +514,18 @@ void pkvm_pgtable_stage2_destroy_range(struct kvm_pgtable *pgt, > kvm->arch.pkvm.is_dying = true; > } > > - if (kvm_vm_is_protected(kvm)) > - __pkvm_pgtable_stage2_reclaim(pgt, addr, addr + size); > - else > - __pkvm_pgtable_stage2_unshare(pgt, addr, addr + size); > + /* Called once for the whole IPA space, so reschedule between mappings */ > + for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) { > + u64 start = __pkvm_mapping_start(mapping); > + u64 end = __pkvm_mapping_end(mapping) + 1; __pkvm_mapping_* are rb-tree internals. I think it is better to use explicitly: start = gfn_to_gpa(mapping->gfn); end = start + (mapping->nr_pages * PAGE_SIZE) Also, I wonder if we'd better WARN if the mapping isn't aligned with the destroyed range? -- Vincent > + > + if (kvm_vm_is_protected(kvm)) > + __pkvm_pgtable_stage2_reclaim(pgt, start, end); > + else > + __pkvm_pgtable_stage2_unshare(pgt, start, end); > + > + cond_resched(); > + } > } > > void pkvm_pgtable_stage2_destroy_pgd(struct kvm_pgtable *pgt) > -- > 2.47.3 > >