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[35.204.162.40]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac7c013ec0esm108015266b.98.2025.04.03.08.27.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Apr 2025 08:27:18 -0700 (PDT) Date: Thu, 3 Apr 2025 15:27:15 +0000 From: Quentin Perret To: Vincent Donnefort Cc: maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 2/9] KVM: arm64: Add a range to __pkvm_host_share_guest() Message-ID: References: <20250306110038.3733649-1-vdonnefort@google.com> <20250306110038.3733649-3-vdonnefort@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250306110038.3733649-3-vdonnefort@google.com> On Thursday 06 Mar 2025 at 11:00:31 (+0000), Vincent Donnefort wrote: > +int __pkvm_host_share_guest(u64 pfn, u64 gfn, u64 nr_pages, struct pkvm_hyp_vcpu *vcpu, > enum kvm_pgtable_prot prot) > { > struct pkvm_hyp_vm *vm = pkvm_hyp_vcpu_to_hyp_vm(vcpu); > u64 phys = hyp_pfn_to_phys(pfn); > u64 ipa = hyp_pfn_to_phys(gfn); > + enum pkvm_page_state state; > struct hyp_page *page; > + u64 size; > int ret; > > if (prot & ~KVM_PGTABLE_PROT_RWX) > return -EINVAL; > > - ret = check_range_allowed_memory(phys, phys + PAGE_SIZE); > + ret = __guest_check_transition_size(phys, ipa, nr_pages, &size); > + if (ret) > + return ret; > + > + ret = check_range_allowed_memory(phys, phys + size); > if (ret) > return ret; > > host_lock_component(); > guest_lock_component(vm); > > - ret = __guest_check_page_state_range(vcpu, ipa, PAGE_SIZE, PKVM_NOPAGE); > + ret = __guest_check_page_state_range(vm, ipa, size, PKVM_NOPAGE); > if (ret) > goto unlock; > > - page = hyp_phys_to_page(phys); > - switch (page->host_state) { > + state = hyp_phys_to_page(phys)->host_state; > + for_each_hyp_page(phys, size, page) { > + if (page->host_state != state) { > + ret = -EPERM; > + goto unlock; > + } > + } > + > + switch (state) { > case PKVM_PAGE_OWNED: > - WARN_ON(__host_set_page_state_range(phys, PAGE_SIZE, PKVM_PAGE_SHARED_OWNED)); > + WARN_ON(__host_set_page_state_range(phys, size, PKVM_PAGE_SHARED_OWNED)); > break; > case PKVM_PAGE_SHARED_OWNED: > - if (page->host_share_guest_count) > - break; > - /* Only host to np-guest multi-sharing is tolerated */ > - WARN_ON(1); > - fallthrough; > + for_each_hyp_page(phys, size, page) { > + /* Only host to np-guest multi-sharing is tolerated */ > + if (WARN_ON(!page->host_share_guest_count)) { > + ret = -EPERM; > + goto unlock; > + } > + } > + break; > default: > ret = -EPERM; > goto unlock; > } > > - WARN_ON(kvm_pgtable_stage2_map(&vm->pgt, ipa, PAGE_SIZE, phys, > + WARN_ON(kvm_pgtable_stage2_map(&vm->pgt, ipa, size, phys, > pkvm_mkstate(prot, PKVM_PAGE_SHARED_BORROWED), > &vcpu->vcpu.arch.pkvm_memcache, 0)); > - page->host_share_guest_count++; > + __host_update_share_guest_count(phys, size, true); So we're walking the entire phys range 3 times; 1. to check the host_state is consistent with that of the first page; 2. to set the state to SHARED_OWNED or to check the host_share_guest_count; 3. and then again here to update the host share guest count I feel like we could probably remove at least one loop with a pattern like so: for_each_hyp_page(phys, size, page) { switch (page->state) { case PKVM_PAGE_OWNED: continue; case PKVM_PAGE_SHARED_BORROWED: if (page->host_shared_guest_count) continue; fallthrough; default; ret = -EPERM; goto unlock; } } for_each_hyp_page(phys, size, page) { page->host_state = PKVM_PAGE_SHARED_OWNED; page->host_share_guest_count++; } That would also tolerate a mix of OWNED and SHARED_OWNED page in the range, which I'm not sure is needed but it doesn't cost us anything to support so ... :-) Wdyt? > unlock: > guest_unlock_component(vm); > diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c > index 930b677eb9b0..00fd9a524bf7 100644 > --- a/arch/arm64/kvm/pkvm.c > +++ b/arch/arm64/kvm/pkvm.c > @@ -361,7 +361,7 @@ int pkvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, > return -EINVAL; > > lockdep_assert_held_write(&kvm->mmu_lock); > - ret = kvm_call_hyp_nvhe(__pkvm_host_share_guest, pfn, gfn, prot); > + ret = kvm_call_hyp_nvhe(__pkvm_host_share_guest, pfn, gfn, 1, prot); > if (ret) { > /* Is the gfn already mapped due to a racing vCPU? */ > if (ret == -EPERM) > -- > 2.48.1.711.g2feabab25a-goog >