[PATCH v3 20/23] KVM: Allow for different capacities in kvm_mmu_memory_cache structs
Anup Patel
anup at brainfault.org
Wed Apr 20 03:55:43 PDT 2022
On Fri, Apr 1, 2022 at 11:26 PM David Matlack <dmatlack at google.com> wrote:
>
> Allow the capacity of the kvm_mmu_memory_cache struct to be chosen at
> declaration time rather than being fixed for all declarations. This will
> be used in a follow-up commit to declare an cache in x86 with a capacity
> of 512+ objects without having to increase the capacity of all caches in
> KVM.
>
> This change requires each cache now specify its capacity at runtime,
> since the cache struct itself no longer has a fixed capacity known at
> compile time. To protect against someone accidentally defining a
> kvm_mmu_memory_cache struct directly (without the extra storage), this
> commit includes a WARN_ON() in kvm_mmu_topup_memory_cache().
>
> This change, unfortunately, adds some grottiness to
> kvm_phys_addr_ioremap() in arm64, which uses a function-local (i.e.
> stack-allocated) kvm_mmu_memory_cache struct. Since C does not allow
> anonymous structs in functions, the new wrapper struct that contains
> kvm_mmu_memory_cache and the objects pointer array, must be named, which
> means dealing with an outer and inner struct. The outer struct can't be
> dropped since then there would be no guarantee the kvm_mmu_memory_cache
> struct and objects array would be laid out consecutively on the stack.
>
> No functional change intended.
>
> Signed-off-by: David Matlack <dmatlack at google.com>
Looks good to me.
For KVM RISC-V:
Acked-by: Anup Patel <anup at brainfault.org>
Regards,
Anup
> ---
> arch/arm64/include/asm/kvm_host.h | 2 +-
> arch/arm64/kvm/arm.c | 1 +
> arch/arm64/kvm/mmu.c | 13 +++++++++----
> arch/mips/include/asm/kvm_host.h | 2 +-
> arch/mips/kvm/mips.c | 2 ++
> arch/riscv/include/asm/kvm_host.h | 2 +-
> arch/riscv/kvm/mmu.c | 17 ++++++++++-------
> arch/riscv/kvm/vcpu.c | 1 +
> arch/x86/include/asm/kvm_host.h | 8 ++++----
> arch/x86/kvm/mmu/mmu.c | 9 +++++++++
> include/linux/kvm_types.h | 19 +++++++++++++++++--
> virt/kvm/kvm_main.c | 10 +++++++++-
> 12 files changed, 65 insertions(+), 21 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 0e96087885fe..4670491899de 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -362,7 +362,7 @@ struct kvm_vcpu_arch {
> bool pause;
>
> /* Cache some mmu pages needed inside spinlock regions */
> - struct kvm_mmu_memory_cache mmu_page_cache;
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_page_cache);
>
> /* Target CPU and feature flags */
> int target;
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index ba9165e84396..af4d8a490af5 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -320,6 +320,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> vcpu->arch.target = -1;
> bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
>
> + vcpu->arch.mmu_page_cache.capacity = KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
>
> /* Set up the timer */
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 0d19259454d8..01e15bcb7be2 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -764,7 +764,12 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> {
> phys_addr_t addr;
> int ret = 0;
> - struct kvm_mmu_memory_cache cache = { 0, __GFP_ZERO, NULL, };
> + DEFINE_KVM_MMU_MEMORY_CACHE(cache) page_cache = {
> + .cache = {
> + .gfp_zero = __GFP_ZERO,
> + .capacity = KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE,
> + },
> + };
> struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_DEVICE |
> KVM_PGTABLE_PROT_R |
> @@ -777,14 +782,14 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> guest_ipa &= PAGE_MASK;
>
> for (addr = guest_ipa; addr < guest_ipa + size; addr += PAGE_SIZE) {
> - ret = kvm_mmu_topup_memory_cache(&cache,
> + ret = kvm_mmu_topup_memory_cache(&page_cache.cache,
> kvm_mmu_cache_min_pages(kvm));
> if (ret)
> break;
>
> write_lock(&kvm->mmu_lock);
> ret = kvm_pgtable_stage2_map(pgt, addr, PAGE_SIZE, pa, prot,
> - &cache);
> + &page_cache.cache);
> write_unlock(&kvm->mmu_lock);
> if (ret)
> break;
> @@ -792,7 +797,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> pa += PAGE_SIZE;
> }
>
> - kvm_mmu_free_memory_cache(&cache);
> + kvm_mmu_free_memory_cache(&page_cache.cache);
> return ret;
> }
>
> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> index 717716cc51c5..935511d7fc3a 100644
> --- a/arch/mips/include/asm/kvm_host.h
> +++ b/arch/mips/include/asm/kvm_host.h
> @@ -347,7 +347,7 @@ struct kvm_vcpu_arch {
> unsigned long pending_exceptions_clr;
>
> /* Cache some mmu pages needed inside spinlock regions */
> - struct kvm_mmu_memory_cache mmu_page_cache;
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_page_cache);
>
> /* vcpu's vzguestid is different on each host cpu in an smp system */
> u32 vzguestid[NR_CPUS];
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index a25e0b73ee70..45c7179144dc 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -387,6 +387,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> if (err)
> goto out_free_gebase;
>
> + vcpu->arch.mmu_page_cache.capacity = KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> +
> return 0;
>
> out_free_gebase:
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index 78da839657e5..4ec0b7a3d515 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -186,7 +186,7 @@ struct kvm_vcpu_arch {
> struct kvm_sbi_context sbi_context;
>
> /* Cache pages needed to program page tables with spinlock held */
> - struct kvm_mmu_memory_cache mmu_page_cache;
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_page_cache);
>
> /* VCPU power-off state */
> bool power_off;
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index f80a34fbf102..5ffd164a5aeb 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -347,10 +347,12 @@ static int stage2_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa,
> int ret = 0;
> unsigned long pfn;
> phys_addr_t addr, end;
> - struct kvm_mmu_memory_cache pcache;
> -
> - memset(&pcache, 0, sizeof(pcache));
> - pcache.gfp_zero = __GFP_ZERO;
> + DEFINE_KVM_MMU_MEMORY_CACHE(cache) page_cache = {
> + .cache = {
> + .gfp_zero = __GFP_ZERO,
> + .capacity = KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE,
> + },
> + };
>
> end = (gpa + size + PAGE_SIZE - 1) & PAGE_MASK;
> pfn = __phys_to_pfn(hpa);
> @@ -361,12 +363,13 @@ static int stage2_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa,
> if (!writable)
> pte = pte_wrprotect(pte);
>
> - ret = kvm_mmu_topup_memory_cache(&pcache, stage2_pgd_levels);
> + ret = kvm_mmu_topup_memory_cache(&page_cache.cache,
> + stage2_pgd_levels);
> if (ret)
> goto out;
>
> spin_lock(&kvm->mmu_lock);
> - ret = stage2_set_pte(kvm, 0, &pcache, addr, &pte);
> + ret = stage2_set_pte(kvm, 0, &page_cache.cache, addr, &pte);
> spin_unlock(&kvm->mmu_lock);
> if (ret)
> goto out;
> @@ -375,7 +378,7 @@ static int stage2_ioremap(struct kvm *kvm, gpa_t gpa, phys_addr_t hpa,
> }
>
> out:
> - kvm_mmu_free_memory_cache(&pcache);
> + kvm_mmu_free_memory_cache(&page_cache.cache);
> return ret;
> }
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 624166004e36..6a5f5aa45bac 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -94,6 +94,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>
> /* Mark this VCPU never ran */
> vcpu->arch.ran_atleast_once = false;
> + vcpu->arch.mmu_page_cache.capacity = KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
>
> /* Setup ISA features available to VCPU */
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index be4349c9ffea..ffb2b99f3a60 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -694,10 +694,10 @@ struct kvm_vcpu_arch {
> */
> struct kvm_mmu *walk_mmu;
>
> - struct kvm_mmu_memory_cache mmu_pte_list_desc_cache;
> - struct kvm_mmu_memory_cache mmu_shadow_page_cache;
> - struct kvm_mmu_memory_cache mmu_shadowed_info_cache;
> - struct kvm_mmu_memory_cache mmu_page_header_cache;
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_pte_list_desc_cache);
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_shadow_page_cache);
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_shadowed_info_cache);
> + DEFINE_KVM_MMU_MEMORY_CACHE(mmu_page_header_cache);
>
> /*
> * QEMU userspace and the guest each have their own FPU state.
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index f058f28909ea..a8200b3f8782 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5800,12 +5800,21 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
> {
> int ret;
>
> + vcpu->arch.mmu_pte_list_desc_cache.capacity =
> + KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> vcpu->arch.mmu_pte_list_desc_cache.kmem_cache = pte_list_desc_cache;
> vcpu->arch.mmu_pte_list_desc_cache.gfp_zero = __GFP_ZERO;
>
> + vcpu->arch.mmu_page_header_cache.capacity =
> + KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
> vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
>
> + vcpu->arch.mmu_shadowed_info_cache.capacity =
> + KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> +
> + vcpu->arch.mmu_shadow_page_cache.capacity =
> + KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE;
> vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
>
> vcpu->arch.mmu = &vcpu->arch.root_mmu;
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index ac1ebb37a0ff..579cf39986ec 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -83,14 +83,29 @@ struct gfn_to_pfn_cache {
> * MMU flows is problematic, as is triggering reclaim, I/O, etc... while
> * holding MMU locks. Note, these caches act more like prefetch buffers than
> * classical caches, i.e. objects are not returned to the cache on being freed.
> + *
> + * The storage for the cache object pointers is laid out after the struct, to
> + * allow different declarations to choose different capacities. The capacity
> + * field defines the number of object pointers available after the struct.
> */
> struct kvm_mmu_memory_cache {
> int nobjs;
> + int capacity;
> gfp_t gfp_zero;
> struct kmem_cache *kmem_cache;
> - void *objects[KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE];
> + void *objects[];
> };
> -#endif
> +
> +#define __DEFINE_KVM_MMU_MEMORY_CACHE(_name, _capacity) \
> + struct { \
> + struct kvm_mmu_memory_cache _name; \
> + void *_name##_objects[_capacity]; \
> + }
> +
> +#define DEFINE_KVM_MMU_MEMORY_CACHE(_name) \
> + __DEFINE_KVM_MMU_MEMORY_CACHE(_name, KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE)
> +
> +#endif /* KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE */
>
> #define HALT_POLL_HIST_COUNT 32
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 70e05af5ebea..c4cac4195f4a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -373,9 +373,17 @@ int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min)
> {
> void *obj;
>
> + /*
> + * The capacity fieldmust be initialized since the storage for the
> + * objects pointer array is laid out after the kvm_mmu_memory_cache
> + * struct and not known at compile time.
> + */
> + if (WARN_ON(mc->capacity == 0))
> + return -EINVAL;
> +
> if (mc->nobjs >= min)
> return 0;
> - while (mc->nobjs < ARRAY_SIZE(mc->objects)) {
> + while (mc->nobjs < mc->capacity) {
> obj = mmu_memory_cache_alloc_obj(mc, GFP_KERNEL_ACCOUNT);
> if (!obj)
> return mc->nobjs >= min ? 0 : -ENOMEM;
> --
> 2.35.1.1094.g7c7d902a7c-goog
>
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