[PATCH v10 29/59] KVM: arm64: nv: Unmap/flush shadow stage 2 page tables
Ganapatrao Kulkarni
gankulkarni at os.amperecomputing.com
Thu Sep 14 06:10:48 PDT 2023
Hi Marc,
On 15-05-2023 11:00 pm, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall at linaro.org>
>
> Unmap/flush shadow stage 2 page tables for the nested VMs as well as the
> stage 2 page table for the guest hypervisor.
>
> Note: A bunch of the code in mmu.c relating to MMU notifiers is
> currently dealt with in an extremely abrupt way, for example by clearing
> out an entire shadow stage-2 table. This will be handled in a more
> efficient way using the reverse mapping feature in a later version of
> the patch series.
We are seeing spin-lock contention due to this patch when the
Guest-Hypervisor(L1) is booted with higher number of cores and auto-numa
is enabled on L0.
kvm_nested_s2_unmap is called as part of notifier call-back when numa
page migration is happening and this function which holds lock becomes
source of contention when there are more vCPUs are processing the
auto-numa page fault/migration.
>
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Jintack Lim <jintack.lim at linaro.org>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
> arch/arm64/include/asm/kvm_mmu.h | 3 +++
> arch/arm64/include/asm/kvm_nested.h | 3 +++
> arch/arm64/kvm/mmu.c | 30 ++++++++++++++++++----
> arch/arm64/kvm/nested.c | 39 +++++++++++++++++++++++++++++
> 4 files changed, 70 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 896acdf98e71..d155b3871c4c 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -169,6 +169,8 @@ int create_hyp_io_mappings(phys_addr_t phys_addr, size_t size,
> void __iomem **haddr);
> int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,
> void **haddr);
> +void kvm_stage2_flush_range(struct kvm_s2_mmu *mmu,
> + phys_addr_t addr, phys_addr_t end);
> void __init free_hyp_pgds(void);
>
> void kvm_unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size);
> @@ -177,6 +179,7 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
> void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu);
> int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> phys_addr_t pa, unsigned long size, bool writable);
> +void kvm_stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end);
>
> int kvm_handle_guest_abort(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> index f20d272fcd6d..d330b947d48a 100644
> --- a/arch/arm64/include/asm/kvm_nested.h
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -111,6 +111,9 @@ extern int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
> extern int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu,
> struct kvm_s2_trans *trans);
> extern int kvm_inject_s2_fault(struct kvm_vcpu *vcpu, u64 esr_el2);
> +extern void kvm_nested_s2_wp(struct kvm *kvm);
> +extern void kvm_nested_s2_unmap(struct kvm *kvm);
> +extern void kvm_nested_s2_flush(struct kvm *kvm);
> int handle_wfx_nested(struct kvm_vcpu *vcpu, bool is_wfe);
>
> extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 1e19c59b8235..8144bb9b9ec8 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -245,13 +245,19 @@ void kvm_unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
> __unmap_stage2_range(mmu, start, size, true);
> }
>
> +void kvm_stage2_flush_range(struct kvm_s2_mmu *mmu,
> + phys_addr_t addr, phys_addr_t end)
> +{
> + stage2_apply_range_resched(mmu, addr, end, kvm_pgtable_stage2_flush);
> +}
> +
> static void stage2_flush_memslot(struct kvm *kvm,
> struct kvm_memory_slot *memslot)
> {
> phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
> phys_addr_t end = addr + PAGE_SIZE * memslot->npages;
>
> - stage2_apply_range_resched(&kvm->arch.mmu, addr, end, kvm_pgtable_stage2_flush);
> + kvm_stage2_flush_range(&kvm->arch.mmu, addr, end);
> }
>
> /**
> @@ -274,6 +280,8 @@ static void stage2_flush_vm(struct kvm *kvm)
> kvm_for_each_memslot(memslot, bkt, slots)
> stage2_flush_memslot(kvm, memslot);
>
> + kvm_nested_s2_flush(kvm);
> +
> write_unlock(&kvm->mmu_lock);
> srcu_read_unlock(&kvm->srcu, idx);
> }
> @@ -888,6 +896,8 @@ void stage2_unmap_vm(struct kvm *kvm)
> kvm_for_each_memslot(memslot, bkt, slots)
> stage2_unmap_memslot(kvm, memslot);
>
> + kvm_nested_s2_unmap(kvm);
> +
> write_unlock(&kvm->mmu_lock);
> mmap_read_unlock(current->mm);
> srcu_read_unlock(&kvm->srcu, idx);
> @@ -987,12 +997,12 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> }
>
> /**
> - * stage2_wp_range() - write protect stage2 memory region range
> + * kvm_stage2_wp_range() - write protect stage2 memory region range
> * @mmu: The KVM stage-2 MMU pointer
> * @addr: Start address of range
> * @end: End address of range
> */
> -static void stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end)
> +void kvm_stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end)
> {
> stage2_apply_range_resched(mmu, addr, end, kvm_pgtable_stage2_wrprotect);
> }
> @@ -1023,7 +1033,8 @@ static void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
> end = (memslot->base_gfn + memslot->npages) << PAGE_SHIFT;
>
> write_lock(&kvm->mmu_lock);
> - stage2_wp_range(&kvm->arch.mmu, start, end);
> + kvm_stage2_wp_range(&kvm->arch.mmu, start, end);
> + kvm_nested_s2_wp(kvm);
> write_unlock(&kvm->mmu_lock);
> kvm_flush_remote_tlbs(kvm);
> }
> @@ -1047,7 +1058,7 @@ static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
> phys_addr_t start = (base_gfn + __ffs(mask)) << PAGE_SHIFT;
> phys_addr_t end = (base_gfn + __fls(mask) + 1) << PAGE_SHIFT;
>
> - stage2_wp_range(&kvm->arch.mmu, start, end);
> + kvm_stage2_wp_range(&kvm->arch.mmu, start, end);
> }
>
> /*
> @@ -1062,6 +1073,7 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
> gfn_t gfn_offset, unsigned long mask)
> {
> kvm_mmu_write_protect_pt_masked(kvm, slot, gfn_offset, mask);
> + kvm_nested_s2_wp(kvm);
> }
>
> static void kvm_send_hwpoison_signal(unsigned long address, short lsb)
> @@ -1720,6 +1732,7 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
> (range->end - range->start) << PAGE_SHIFT,
> range->may_block);
>
> + kvm_nested_s2_unmap(kvm);
This kvm_nested_s2_unmap/kvm_unmap_stage2_range is called for every
active L2 and page table walk-through iterates for long iterations since
kvm_phys_size(mmu) is pretty big size(atleast 48bits).
What would be the best fix if we want to avoid this unnessary long
iteration of page table lookup?
> return false;
> }
>
> @@ -1754,6 +1767,7 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> PAGE_SIZE, __pfn_to_phys(pfn),
> KVM_PGTABLE_PROT_R, NULL, 0);
>
> + kvm_nested_s2_unmap(kvm);
> return false;
> }
>
> @@ -1772,6 +1786,11 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> range->start << PAGE_SHIFT);
> pte = __pte(kpte);
> return pte_valid(pte) && pte_young(pte);
> +
> + /*
> + * TODO: Handle nested_mmu structures here using the reverse mapping in
> + * a later version of patch series.
> + */
> }
>
> bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> @@ -2004,6 +2023,7 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
>
> write_lock(&kvm->mmu_lock);
> kvm_unmap_stage2_range(&kvm->arch.mmu, gpa, size);
> + kvm_nested_s2_unmap(kvm);
> write_unlock(&kvm->mmu_lock);
> }
>
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 73c0be25345a..948ac5b9638c 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -523,6 +523,45 @@ int kvm_inject_s2_fault(struct kvm_vcpu *vcpu, u64 esr_el2)
> return kvm_inject_nested_sync(vcpu, esr_el2);
> }
>
> +/* expects kvm->mmu_lock to be held */
> +void kvm_nested_s2_wp(struct kvm *kvm)
> +{
> + int i;
> +
> + for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
> + struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
> +
> + if (kvm_s2_mmu_valid(mmu))
> + kvm_stage2_wp_range(mmu, 0, kvm_phys_size(mmu));
> + }
> +}
> +
> +/* expects kvm->mmu_lock to be held */
> +void kvm_nested_s2_unmap(struct kvm *kvm)
> +{
> + int i;
> +
> + for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
> + struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
> +
> + if (kvm_s2_mmu_valid(mmu))
> + kvm_unmap_stage2_range(mmu, 0, kvm_phys_size(mmu));
> + }
> +}
> +
> +/* expects kvm->mmu_lock to be held */
> +void kvm_nested_s2_flush(struct kvm *kvm)
> +{
> + int i;
> +
> + for (i = 0; i < kvm->arch.nested_mmus_size; i++) {
> + struct kvm_s2_mmu *mmu = &kvm->arch.nested_mmus[i];
> +
> + if (kvm_s2_mmu_valid(mmu))
> + kvm_stage2_flush_range(mmu, 0, kvm_phys_size(mmu));
> + }
> +}
> +
> void kvm_arch_flush_shadow_all(struct kvm *kvm)
> {
> int i;
Thanks,
Ganapat
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