[PATCH RESEND v15 07/10] KVM: arm: page logging 2nd stage fault handling
Christoffer Dall
christoffer.dall at linaro.org
Sun Jan 11 06:00:03 PST 2015
On Fri, Jan 09, 2015 at 08:17:20PM -0800, Mario Smarduch wrote:
> This patch adds support for 2nd stage page fault handling while dirty page
> logging. On huge page faults, huge pages are dissolved to normal pages, and
> rebuilding of 2nd stage huge pages is blocked. In case migration is
> canceled this restriction is removed and huge pages may be rebuilt again.
>
> This patch applies cleanly on top of patch series posted Dec. 15'th:
> https://lists.cs.columbia.edu/pipermail/kvmarm/2014-December/012826.html
In the future such information should also go under the ---
separator.
>
> Patch #11 has been dropped, and should not be applied.
this should go under the '---' separator too.
>
> Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
> ---
>
> Change Log since last RESEND v1 --> v2:
> - Disallow dirty page logging of IO region - fail for initial write protect
> and disable logging code in 2nd stage page fault handler.
> - Fixed auto spell correction errors
>
> Change Log RESEND v0 --> v1:
> - fixed bug exposed by new generic __get_user_pages_fast(), when region is
> writable, prevent write protection of pte on read fault
> - Removed marking entire huge page dirty on initial access
> - don't dissolve huge pages of non-writable regions
> - Made updates based on Christoffers comments
> - renamed logging status function to memslot_is_logging()
> - changed few values to bool from longs
> - streamlined user_mem_abort() to eliminate extra conditional checks
> ---
> arch/arm/kvm/mmu.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 105 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 73d506f..b878236 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -47,6 +47,18 @@ static phys_addr_t hyp_idmap_vector;
> #define kvm_pmd_huge(_x) (pmd_huge(_x) || pmd_trans_huge(_x))
> #define kvm_pud_huge(_x) pud_huge(_x)
>
> +#define KVM_S2PTE_FLAG_IS_IOMAP (1UL << 0)
> +#define KVM_S2PTE_FLAG_LOGGING_ACTIVE (1UL << 1)
> +
> +static bool memslot_is_logging(struct kvm_memory_slot *memslot)
> +{
> +#ifdef CONFIG_ARM
> + return !!memslot->dirty_bitmap;
> +#else
> + return false;
> +#endif
> +}
> +
> static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> {
> /*
> @@ -59,6 +71,25 @@ static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, kvm, ipa);
> }
>
> +/**
> + * stage2_dissolve_pmd() - clear and flush huge PMD entry
> + * @kvm: pointer to kvm structure.
> + * @addr: IPA
> + * @pmd: pmd pointer for IPA
> + *
> + * Function clears a PMD entry, flushes addr 1st and 2nd stage TLBs. Marks all
> + * pages in the range dirty.
> + */
> +static void stage2_dissolve_pmd(struct kvm *kvm, phys_addr_t addr, pmd_t *pmd)
> +{
> + if (!kvm_pmd_huge(*pmd))
> + return;
> +
> + pmd_clear(pmd);
> + kvm_tlb_flush_vmid_ipa(kvm, addr);
> + put_page(virt_to_page(pmd));
> +}
> +
> static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
> int min, int max)
> {
> @@ -703,10 +734,13 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
> }
>
> static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> - phys_addr_t addr, const pte_t *new_pte, bool iomap)
> + phys_addr_t addr, const pte_t *new_pte,
> + unsigned long flags)
> {
> pmd_t *pmd;
> pte_t *pte, old_pte;
> + bool iomap = flags & KVM_S2PTE_FLAG_IS_IOMAP;
> + bool logging_active = flags & KVM_S2PTE_FLAG_LOGGING_ACTIVE;
>
> /* Create stage-2 page table mapping - Levels 0 and 1 */
> pmd = stage2_get_pmd(kvm, cache, addr);
> @@ -718,6 +752,13 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> return 0;
> }
>
> + /*
> + * While dirty page logging - dissolve huge PMD, then continue on to
> + * allocate page.
> + */
> + if (logging_active)
> + stage2_dissolve_pmd(kvm, addr, pmd);
> +
> /* Create stage-2 page mappings - Level 2 */
> if (pmd_none(*pmd)) {
> if (!cache)
> @@ -774,7 +815,8 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> if (ret)
> goto out;
> spin_lock(&kvm->mmu_lock);
> - ret = stage2_set_pte(kvm, &cache, addr, &pte, true);
> + ret = stage2_set_pte(kvm, &cache, addr, &pte,
> + KVM_S2PTE_FLAG_IS_IOMAP);
> spin_unlock(&kvm->mmu_lock);
> if (ret)
> goto out;
> @@ -1002,6 +1044,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> pfn_t pfn;
> pgprot_t mem_type = PAGE_S2;
> bool fault_ipa_uncached;
> + bool can_set_pte_rw = true;
> + unsigned long set_pte_flags = 0;
>
> write_fault = kvm_is_write_fault(vcpu);
> if (fault_status == FSC_PERM && !write_fault) {
> @@ -1009,6 +1053,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> +
stray whitespace change?
> /* Let's check if we will get back a huge page backed by hugetlbfs */
> down_read(¤t->mm->mmap_sem);
> vma = find_vma_intersection(current->mm, hva, hva + 1);
> @@ -1059,12 +1104,35 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (is_error_pfn(pfn))
> return -EFAULT;
>
> - if (kvm_is_device_pfn(pfn))
> + if (kvm_is_device_pfn(pfn)) {
> mem_type = PAGE_S2_DEVICE;
> + set_pte_flags = KVM_S2PTE_FLAG_IS_IOMAP;
> + }
>
> spin_lock(&kvm->mmu_lock);
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
> +
> + /*
> + * When logging is enabled general page fault handling changes:
> + * - Writable huge pages are dissolved on a read or write fault.
why dissolve huge pages on a read fault?
> + * - pte's are not allowed write permission on a read fault to
> + * writable region so future writes can be marked dirty
new line
> + * Access to non-writable region is unchanged, and logging of IO
> + * regions is not allowed.
> + */
> + if (memslot_is_logging(memslot) && writable) {
> + set_pte_flags = KVM_S2PTE_FLAG_LOGGING_ACTIVE;
> + if (hugetlb) {
> + gfn += pte_index(fault_ipa);
> + pfn += pte_index(fault_ipa);
> + hugetlb = false;
> + }
> + force_pte = true;
uh, not this is not what I meant, see my example (untested, partial)
patch in the end of this mail.
> + if (!write_fault)
> + can_set_pte_rw = false;
> + }
> +
> if (!hugetlb && !force_pte)
> hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>
> @@ -1082,16 +1150,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
> } else {
> pte_t new_pte = pfn_pte(pfn, mem_type);
> - if (writable) {
> +
> + /*
> + * Don't set write permission, for non-writable region, and
> + * for read fault to writable region while logging.
> + */
> + if (writable && can_set_pte_rw) {
> kvm_set_s2pte_writable(&new_pte);
> kvm_set_pfn_dirty(pfn);
> }
> coherent_cache_guest_page(vcpu, hva, PAGE_SIZE,
> fault_ipa_uncached);
> ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte,
> - pgprot_val(mem_type) == pgprot_val(PAGE_S2_DEVICE));
> + set_pte_flags);
> }
>
> + if (write_fault)
> + mark_page_dirty(kvm, gfn);
>
> out_unlock:
> spin_unlock(&kvm->mmu_lock);
> @@ -1242,7 +1317,14 @@ static void kvm_set_spte_handler(struct kvm *kvm, gpa_t gpa, void *data)
> {
> pte_t *pte = (pte_t *)data;
>
> - stage2_set_pte(kvm, NULL, gpa, pte, false);
> + /*
> + * We can always call stage2_set_pte with KVM_S2PTE_FLAG_LOGGING_ACTIVE
> + * flag clear because MMU notifiers will have unmapped a huge PMD before
> + * calling ->change_pte() (which in turn calls kvm_set_spte_hva()) and
> + * therefore stage2_set_pte() never needs to clear out a huge PMD
> + * through this calling path.
> + */
> + stage2_set_pte(kvm, NULL, gpa, pte, 0);
> }
>
>
> @@ -1396,7 +1478,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
> bool writable = !(mem->flags & KVM_MEM_READONLY);
> int ret = 0;
>
> - if (change != KVM_MR_CREATE && change != KVM_MR_MOVE)
> + /*
> + * Let - enable of dirty page logging through, later check if it's for
> + * an IO region and fail.
> + */
I don't understand this comment or find it helpful.
> + if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
> + change == KVM_MR_FLAGS_ONLY &&
> + !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES))
this looks wrong, because you can now remove all the other checks of
change != and you are not returning early for KVM_MR_DELETE.
I think you want to add a check simply for 'change != KVM_MR_FLAGS_ONLY'
and then after the 'return 0' check the subconditions for change ==
KVM_MR_FLAGS_ONLY.
> return 0;
>
> /*
> @@ -1447,15 +1535,24 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
> phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) +
> vm_start - vma->vm_start;
>
> - ret = kvm_phys_addr_ioremap(kvm, gpa, pa,
> + if (change != KVM_MR_FLAGS_ONLY)
> + ret = kvm_phys_addr_ioremap(kvm, gpa, pa,
> vm_end - vm_start,
> writable);
> + else
> + /* IO region dirty page logging not allowed */
> + return -EINVAL;
> +
this whole thing also looks weird. I think you just need to add a check
before kvm_phys_addr_ioremap() for flags & KVM_MEM_LOG_DIRTY_PAGES and
return an error in that case (you've identified a user attempting to set
dirty page logging on something that points to device memory, it doesn't
matter at this point through which 'change' it is done).
> if (ret)
> break;
> }
> hva = vm_end;
> } while (hva < reg_end);
>
> + /* Anything after here doesn't apply to memslot flag changes */
> + if (change == KVM_MR_FLAGS_ONLY)
> + return ret;
> +
> spin_lock(&kvm->mmu_lock);
> if (ret)
> unmap_stage2_range(kvm, mem->guest_phys_addr, mem->memory_size);
> --
What I meant last time around concerning user_mem_abort was more
something like this:
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 1dc9778..38ea58e 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -935,7 +935,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
return -EFAULT;
}
- if (is_vm_hugetlb_page(vma)) {
+ /*
+ * Writes to pages in a memslot with logging enabled are always logged
+ * on a singe page-by-page basis.
+ */
+ if (memslot_is_logging(memslot) && write_fault)
+ force_pte = true;
+
+ if (is_vm_hugetlb_page(vma) && !force_pte) {
hugetlb = true;
gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
} else {
@@ -976,6 +983,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (is_error_pfn(pfn))
return -EFAULT;
+ if (memslot_is_logging(memslot) && !write_fault)
+ writable = false;
+
if (kvm_is_device_pfn(pfn))
mem_type = PAGE_S2_DEVICE;
@@ -998,15 +1008,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
fault_ipa_uncached);
ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
} else {
+ unsigned long flags = 0;
pte_t new_pte = pfn_pte(pfn, mem_type);
+
if (writable) {
kvm_set_s2pte_writable(&new_pte);
kvm_set_pfn_dirty(pfn);
}
coherent_cache_guest_page(vcpu, hva, PAGE_SIZE,
fault_ipa_uncached);
- ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte,
- pgprot_val(mem_type) == pgprot_val(PAGE_S2_DEVICE));
+
+ if (pgprot_val(mem_type) == pgprot_val(PAGE_S2_DEVICE))
+ flags |= KVM_S2PTE_FLAG_IS_IOMAP;
+
+ if (memslot_is_logging(memslot))
+ flags |= KVM_S2_FLAG_LOGGING_ACTIVE;
+
+ ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, flags);
}
Thanks,
-Christoffer
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