Messages in this thread Patch in this message | | | Subject | Re: [RFC PATCH 1/3] KVM: arm64: Fix possible memory leak in kvm stage2 | From | "wangyanan (Y)" <> | Date | Wed, 2 Dec 2020 01:19:35 +0800 |
| |
On 2020/12/1 22:16, Will Deacon wrote:
> On Tue, Dec 01, 2020 at 03:21:23PM +0800, wangyanan (Y) wrote: >> On 2020/11/30 21:21, Will Deacon wrote: >>> On Mon, Nov 30, 2020 at 08:18:45PM +0800, Yanan Wang wrote: >>>> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c >>>> index 0271b4a3b9fe..696b6aa83faf 100644 >>>> --- a/arch/arm64/kvm/hyp/pgtable.c >>>> +++ b/arch/arm64/kvm/hyp/pgtable.c >>>> @@ -186,6 +186,7 @@ static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr, >>>> return old == pte; >>>> smp_store_release(ptep, pte); >>>> + get_page(virt_to_page(ptep)); >>> This is also used for the hypervisor stage-1 page-table, so I'd prefer to >>> leave this function as-is. >> I agree at this point. >>>> return true; >>>> } >>>> @@ -476,6 +477,7 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >>>> /* There's an existing valid leaf entry, so perform break-before-make */ >>>> kvm_set_invalid_pte(ptep); >>>> kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level); >>>> + put_page(virt_to_page(ptep)); >>>> kvm_set_valid_leaf_pte(ptep, phys, data->attr, level); >>>> out: >>>> data->phys += granule; >>> Isn't this hunk alone sufficient to solve the problem? >>> >>> Will >>> . >> Not sufficient enough. When the old ptep is valid and old pte equlas new >> pte, in this case, "True" is also returned by kvm_set_valid_leaf_pte() >> >> and get_page() will still be called. > I had a go at fixing this without introducing refcounting to the hyp stage-1 > case, and ended up with the diff below. What do you think?
Hi Will,
Functionally this diff looks fine to me. A small comment inline, please see below.
I had made an alternative fix (after sending v1) and it looks much more concise.
If you're ok with it, I can send it as v2 (together with patch#2 and #3) after some tests.
Thanks,
Yanan
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 0271b4a3b9fe..b232bdd142a6 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -470,6 +470,9 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, if (!kvm_block_mapping_supported(addr, end, phys, level)) return false;
+ if (kvm_pte_valid(*ptep)) + put_page(virt_to_page(ptep)); + if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level)) goto out;
> --->8 > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 0271b4a3b9fe..78e2c0dc47ae 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -170,23 +170,16 @@ static void kvm_set_table_pte(kvm_pte_t *ptep, kvm_pte_t *childp) > smp_store_release(ptep, pte); > } > > -static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr, > - u32 level) > +static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level) > { > - kvm_pte_t old = *ptep, pte = kvm_phys_to_pte(pa); > + kvm_pte_t pte = kvm_phys_to_pte(pa); > u64 type = (level == KVM_PGTABLE_MAX_LEVELS - 1) ? KVM_PTE_TYPE_PAGE : > KVM_PTE_TYPE_BLOCK; > > pte |= attr & (KVM_PTE_LEAF_ATTR_LO | KVM_PTE_LEAF_ATTR_HI); > pte |= FIELD_PREP(KVM_PTE_TYPE, type); > pte |= KVM_PTE_VALID; > - > - /* Tolerate KVM recreating the exact same mapping. */ > - if (kvm_pte_valid(old)) > - return old == pte; > - > - smp_store_release(ptep, pte); > - return true; > + return pte; > } > > static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data, u64 addr, > @@ -341,12 +334,17 @@ static int hyp_map_set_prot_attr(enum kvm_pgtable_prot prot, > static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level, > kvm_pte_t *ptep, struct hyp_map_data *data) > { > + kvm_pte_t new, old = *ptep; > u64 granule = kvm_granule_size(level), phys = data->phys; > > if (!kvm_block_mapping_supported(addr, end, phys, level)) > return false; > > - WARN_ON(!kvm_set_valid_leaf_pte(ptep, phys, data->attr, level)); > + /* Tolerate KVM recreating the exact same mapping. */ > + new = kvm_init_valid_leaf_pte(phys, data->attr, level); > + if (old != new && !WARN_ON(kvm_pte_valid(old))) > + smp_store_release(ptep, new); > + > data->phys += granule; > return true; > } > @@ -465,19 +463,24 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, > kvm_pte_t *ptep, > struct stage2_map_data *data) > { > + kvm_pte_t new, old = *ptep; > u64 granule = kvm_granule_size(level), phys = data->phys; > > if (!kvm_block_mapping_supported(addr, end, phys, level)) > return false; > > - if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level)) > - goto out; > + new = kvm_init_valid_leaf_pte(phys, data->attr, level); > + if (kvm_pte_valid(old)) { > + /* > + * There's an existing valid leaf entry, so perform > + * break-before-make. > + */ > + kvm_set_invalid_pte(ptep); > + kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level); > + put_page(virt_to_page(ptep));
When old PTE is valid and equals to the new one, we will also perform break-before-make and the new PTE installation. But they're actually not necessary in this case.
> + } > > - /* There's an existing valid leaf entry, so perform break-before-make */ > - kvm_set_invalid_pte(ptep); > - kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level); > - kvm_set_valid_leaf_pte(ptep, phys, data->attr, level); > -out: > + smp_store_release(ptep, new); > data->phys += granule; > return true; > } > .
| |