Messages in this thread Patches in this message | | | Subject | Re: [RFC PATCH] KVM: arm64: Add prejudgement for relaxing permissions only case in stage2 translation fault handler | From | "wangyanan (Y)" <> | Date | Mon, 14 Dec 2020 15:20:56 +0800 |
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Hi Will, Marc,
On 2020/12/11 18:00, Will Deacon wrote: > On Fri, Dec 11, 2020 at 09:49:28AM +0000, Marc Zyngier wrote: >> On 2020-12-11 08:01, Yanan Wang wrote: >>> @@ -461,25 +462,56 @@ static int stage2_map_set_prot_attr(enum >>> kvm_pgtable_prot prot, >>> return 0; >>> } >>> >>> +static bool stage2_set_valid_leaf_pte_pre(u64 addr, u32 level, >>> + kvm_pte_t *ptep, kvm_pte_t new, >>> + struct stage2_map_data *data) >>> +{ >>> + kvm_pte_t old = *ptep, old_attr, new_attr; >>> + >>> + if ((old ^ new) & (~KVM_PTE_LEAF_ATTR_PERMS)) >>> + return false; >>> + >>> + /* >>> + * Skip updating if we are trying to recreate exactly the same mapping >>> + * or to reduce the access permissions only. And update the valid leaf >>> + * PTE without break-before-make if we are trying to add more access >>> + * permissions only. >>> + */ >>> + old_attr = (old & KVM_PTE_LEAF_ATTR_PERMS) ^ >>> KVM_PTE_LEAF_ATTR_HI_S2_XN; >>> + new_attr = (new & KVM_PTE_LEAF_ATTR_PERMS) ^ >>> KVM_PTE_LEAF_ATTR_HI_S2_XN; >>> + if (new_attr <= old_attr) >>> + return true; >>> + >>> + WRITE_ONCE(*ptep, new); >>> + kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level); >> I think what bothers me the most here is that we are turning a mapping into >> a permission update, which makes the code really hard to read, and mixes >> two things that were so far separate. >> >> I wonder whether we should instead abort the update and simply take the >> fault >> again, if we ever need to do it. > That's a nice idea. If we could enforce that we don't alter permissions on > the map path, and instead just return e.g. -EAGAIN then that would be a > very neat solution and would cement the permission vs translation fault > division.
I agree with that we can indeed simplify the code, separate permission-relaxing and
mapping by the *straightly return* way, although the cost is one more vCPU trap on
permission fault next time possibly.
So how about the new two diffs below? I split them into two patches with different aims.
Thanks,
Yanan.
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 23a01dfcb27a..a74a62283012 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -170,10 +170,9 @@ 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;
@@ -181,12 +180,7 @@ static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr, 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 +335,17 @@ 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; } @@ -465,21 +464,29 @@ 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; + struct page *page = virt_to_page(ptep);
if (!kvm_block_mapping_supported(addr, end, phys, level)) return false;
- if (kvm_pte_valid(*ptep)) - put_page(virt_to_page(ptep)); + new = kvm_init_valid_leaf_pte(phys, data->attr, level); + if (kvm_pte_valid(old)) { + /* Tolerate KVM recreating the exact same mapping. */ + if (old == new) + goto out;
- if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level)) - goto out; + /* There's an existing different 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(page); + }
- /* 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); + smp_store_release(ptep, new); + get_page(page); out: data->phys += granule; return true; @@ -521,7 +528,7 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep, }
if (stage2_map_walker_try_leaf(addr, end, level, ptep, data)) - goto out_get_page; + return 0;
if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1)) return -EINVAL; @@ -545,9 +552,8 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep, }
kvm_set_table_pte(ptep, childp); - -out_get_page: get_page(page); + return 0; }
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index a74a62283012..e3c6133567c4 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -45,6 +45,10 @@
#define KVM_PTE_LEAF_ATTR_HI_S2_XN BIT(54)
+#define KVM_PTE_LEAF_ATTR_S2_PERMS (KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | \ + KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \ + KVM_PTE_LEAF_ATTR_HI_S2_XN) + struct kvm_pgtable_walk_data { struct kvm_pgtable *pgt; struct kvm_pgtable_walker *walker; @@ -473,8 +477,13 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
new = kvm_init_valid_leaf_pte(phys, data->attr, level); if (kvm_pte_valid(old)) { - /* Tolerate KVM recreating the exact same mapping. */ - if (old == new) + /* + * Skip updating the PTE with break-before-make if we are trying + * to recreate the exact same mapping or only change the access + * permissions. Actually, change of permissions will be handled + * through the relax_perms path next time if necessary. + */ + if (!((old ^ new) & (~KVM_PTE_LEAF_ATTR_S2_PERMS))) goto out;
/* There's an existing different valid leaf entry, so perform
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