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[35.233.69.230]) by smtp.gmail.com with ESMTPSA id 1sm1933768wmj.2.2021.03.12.03.45.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Mar 2021 03:45:28 -0800 (PST) Date: Fri, 12 Mar 2021 11:45:26 +0000 From: Quentin Perret To: Will Deacon Subject: Re: [PATCH v4 28/34] KVM: arm64: Use page-table to track page ownership Message-ID: References: <20210310175751.3320106-1-qperret@google.com> <20210310175751.3320106-29-qperret@google.com> <20210311183834.GC31378@willie-the-truck> <20210312093205.GB32016@willie-the-truck> <20210312111804.GB32208@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210312111804.GB32208@willie-the-truck> Cc: android-kvm@google.com, catalin.marinas@arm.com, mate.toth-pal@arm.com, seanjc@google.com, tabba@google.com, linux-kernel@vger.kernel.org, robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org, maz@kernel.org, kernel-team@android.com, kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Friday 12 Mar 2021 at 11:18:05 (+0000), Will Deacon wrote: > On Fri, Mar 12, 2021 at 10:13:26AM +0000, Quentin Perret wrote: > > On Friday 12 Mar 2021 at 09:32:06 (+0000), Will Deacon wrote: > > > I'm not saying to use the VMID directly, just that allocating half of the > > > pte feels a bit OTT given that the state of things after this patch series > > > is that we're using exactly 1 bit. > > > > Right, and that was the reason for the PROT_NONE approach in the > > previous version, but we agreed it'd be worth generalizing to allow for > > future use-cases :-) > > Yeah, just generalising to 32 bits feels like going too far! I dunno, > make it a u8 for now, or define the hypervisor owner ID as 1 and reject > owners greater than that? We can easily extend it later. Alrighty I'll do _both_ > > > > > > @@ -517,28 +543,36 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, > > > > > > if (!kvm_block_mapping_supported(addr, end, phys, level)) > > > > > > return -E2BIG; > > > > > > > > > > > > - new = kvm_init_valid_leaf_pte(phys, data->attr, level); > > > > > > - if (kvm_pte_valid(old)) { > > > > > > + if (kvm_pte_valid(data->attr)) > > > > > > > > > > This feels like a bit of a hack to me: the 'attr' field in stage2_map_data > > > > > is intended to correspond directly to the lower/upper attributes of the > > > > > descriptor as per the architecture, so tagging the valid bit in there is > > > > > pretty grotty. However, I can see the significant advantage in being able > > > > > to re-use the stage2_map_walker functionality, so about instead of nobbling > > > > > attr, you set phys to something invalid instead, e.g.: > > > > > > > > > > #define KVM_PHYS_SET_OWNER (-1ULL) > > > > > > > > That'll confuse kvm_block_mapping_supported() and friends I think, at > > > > least in their current form. If you _really_ don't like this, maybe we > > > > could have an extra 'flags' field in stage2_map_data? > > > > > > I was pondering this last night and I thought of two ways to do it: > > > > > > 1. Add a 'bool valid' and then stick the owner and the phys in a union. > > > (yes, you'll need to update the block mapping checks to look at the > > > valid flag) > > > > Right, though that is also used for the hyp s1 which doesn't use any of > > this ATM. That shouldn't be too bad to change, I'll have a look. > > Oh, I meant stick the bool in the stage2_map_data so that should be limited > to the stage2 path. I mean I still want to use kvm_block_mapping_supported() but ignore the phys check when it's not valid. I find it ugly to add a 'valid' parameter to the function itself, so maybe we're better off with just special casing phys == -1ULL as you first suggested. How much do you hate the below (totally untested)? diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 8e4599256969..9ec937462fd6 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -71,6 +71,13 @@ static u64 kvm_granule_size(u32 level) return BIT(kvm_granule_shift(level)); } +#define KVM_PHYS_INVALID (-1ULL) + +static bool kvm_phys_is_valid(u64 phys) +{ + return phys != KVM_PHYS_INVALID; +} + static bool kvm_level_support_block_mappings(u32 level) { /* @@ -90,7 +97,10 @@ static bool kvm_block_mapping_supported(u64 addr, u64 end, u64 phys, u32 level) if (granule > (end - addr)) return false; - return IS_ALIGNED(addr, granule) && IS_ALIGNED(phys, granule); + if (kvm_phys_is_valid(phys) && !IS_ALIGNED(phys, granule)) + return false; + + return IS_ALIGNED(addr, granule); } static u32 kvm_pgtable_idx(struct kvm_pgtable_walk_data *data, u32 level) @@ -550,7 +560,7 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, if (!kvm_block_mapping_supported(addr, end, phys, level)) return -E2BIG; - if (kvm_pte_valid(data->attr)) + if (kvm_phys_is_valid(phys)) new = kvm_init_valid_leaf_pte(phys, data->attr, level); else new = kvm_init_invalid_leaf_owner(data->owner_id); @@ -580,7 +590,8 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, smp_store_release(ptep, new); if (stage2_pte_is_counted(new)) mm_ops->get_page(ptep); - data->phys += granule; + if (kvm_phys_is_valid(phys)) + data->phys += granule; return 0; } @@ -739,9 +750,6 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, if (ret) return ret; - /* Set the valid flag to distinguish with the set_owner() path. */ - map_data.attr |= KVM_PTE_VALID; - ret = kvm_pgtable_walk(pgt, addr, size, &walker); dsb(ishst); return ret; @@ -752,6 +760,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size, { int ret; struct stage2_map_data map_data = { + .phys = KVM_PHYS_INVALID, .mmu = pgt->mmu, .memcache = mc, .mm_ops = pgt->mm_ops, _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm