On 4/9/23 2:29 PM, Ricardo Koller wrote:
Add a capability for userspace to specify the eager split chunk size.
The chunk size specifies how many pages to break at a time, using a
single allocation. Bigger the chunk size, more pages need to be
allocated ahead of time.
Suggested-by: Oliver Upton <oliver.upton@xxxxxxxxx>
Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 28 ++++++++++++++++++++++++++
arch/arm64/include/asm/kvm_host.h | 15 ++++++++++++++
arch/arm64/include/asm/kvm_pgtable.h | 18 +++++++++++++++++
arch/arm64/kvm/arm.c | 30 ++++++++++++++++++++++++++++
arch/arm64/kvm/mmu.c | 3 +++
include/uapi/linux/kvm.h | 2 ++
6 files changed, 96 insertions(+)
With the following comments addressed:
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 62de0768d6aa5..f8faa80d87057 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8380,6 +8380,34 @@ structure.
When getting the Modified Change Topology Report value, the attr->addr
must point to a byte where the value will be stored or retrieved from.
+8.40 KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE
+---------------------------------------
+
+:Capability: KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE
+:Architectures: arm64
+:Type: vm
+:Parameters: arg[0] is the new split chunk size.
+:Returns: 0 on success, -EINVAL if any memslot was already created.
^^^^^^^^^^^^^^^^^^^
Maybe s/was already created/has been created
+
+This capability sets the chunk size used in Eager Page Splitting.
+
+Eager Page Splitting improves the performance of dirty-logging (used
+in live migrations) when guest memory is backed by huge-pages. It
+avoids splitting huge-pages (into PAGE_SIZE pages) on fault, by doing
+it eagerly when enabling dirty logging (with the
+KVM_MEM_LOG_DIRTY_PAGES flag for a memory region), or when using
+KVM_CLEAR_DIRTY_LOG.
+
+The chunk size specifies how many pages to break at a time, using a
+single allocation for each chunk. Bigger the chunk size, more pages
+need to be allocated ahead of time.
+
+The chunk size needs to be a valid block size. The list of acceptable
+block sizes is exposed in KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES as a 64bit
+bitmap (each bit describing a block size). Setting
+KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE to 0 disables Eager Page Splitting;
+this is the default value.
+
s/a 64bit bitmap/a 64-bit bitmap
For the last sentence, maybe:
The default value is 0, to disable the eager page splitting.
9. Known KVM API problems
=========================
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index a1892a8f60323..b87da1ebc3454 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -158,6 +158,21 @@ struct kvm_s2_mmu {
/* The last vcpu id that ran on each physical CPU */
int __percpu *last_vcpu_ran;
+#define KVM_ARM_EAGER_SPLIT_CHUNK_SIZE_DEFAULT 0
+ /*
+ * Memory cache used to split
+ * KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE worth of huge pages. It
+ * is used to allocate stage2 page tables while splitting huge
+ * pages. Note that the choice of EAGER_PAGE_SPLIT_CHUNK_SIZE
+ * influences both the capacity of the split page cache, and
+ * how often KVM reschedules. Be wary of raising CHUNK_SIZE
+ * too high.
+ *
+ * Protected by kvm->slots_lock.
+ */
+ struct kvm_mmu_memory_cache split_page_cache;
+ uint64_t split_page_chunk_size;
+
struct kvm_arch *arch;
};
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 32e5d42bf020f..889bd7afeb355 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -92,6 +92,24 @@ static inline bool kvm_level_supports_block_mapping(u32 level)
return level >= KVM_PGTABLE_MIN_BLOCK_LEVEL;
}
+static inline u64 kvm_supported_block_sizes(void)
+{
+ u32 level = KVM_PGTABLE_MIN_BLOCK_LEVEL;
+ u64 res = 0;
+
+ for (; level < KVM_PGTABLE_MAX_LEVELS; level++)
+ res |= BIT(kvm_granule_shift(level));
+
+ return res;
+}
+
maybe s/@res/@r
+static inline bool kvm_is_block_size_supported(u64 size)
+{
+ bool is_power_of_two = !((size) & ((size)-1));
+
+ return is_power_of_two && (size & kvm_supported_block_sizes());
+}
+
IS_ALIGNED() maybe used here.
/**
* struct kvm_pgtable_mm_ops - Memory management callbacks.
* @zalloc_page: Allocate a single zeroed memory page.
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 3bd732eaf0872..34fd3c59a9b82 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -67,6 +67,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
struct kvm_enable_cap *cap)
{
int r;
+ u64 new_cap;
if (cap->flags)
return -EINVAL;
@@ -91,6 +92,26 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
r = 0;
set_bit(KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED, &kvm->arch.flags);
break;
+ case KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE:
+ new_cap = cap->args[0];
+
+ mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->slots_lock);
+ /*
+ * To keep things simple, allow changing the chunk
+ * size only if there are no memslots already created.
+ */
/*
* To keep things simple, allow changing the chunk size
* only when no memory slots have been created.
*/
+ if (!kvm_are_all_memslots_empty(kvm)) {
+ r = -EINVAL;
+ } else if (new_cap && !kvm_is_block_size_supported(new_cap)) {
+ r = -EINVAL;
+ } else {
+ r = 0;
+ kvm->arch.mmu.split_page_chunk_size = new_cap;
+ }
+ mutex_unlock(&kvm->slots_lock);
+ mutex_unlock(&kvm->lock);
+ break;
default:
r = -EINVAL;
break;
@@ -288,6 +309,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ARM_PTRAUTH_GENERIC:
r = system_has_full_ptr_auth();
break;
+ case KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE:
+ if (kvm)
+ r = kvm->arch.mmu.split_page_chunk_size;
+ else
+ r = KVM_ARM_EAGER_SPLIT_CHUNK_SIZE_DEFAULT;
+ break;
+ case KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES:
+ r = kvm_supported_block_sizes();
+ break;
kvm_supported_block_sizes() returns u64, but @r is 32-bits in width. It may be
worthy to make the return value from kvm_supported_block_sizes() as u32.
default:
r = 0;
}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a2800e5c42712..898985b09321a 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -756,6 +756,9 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long t
for_each_possible_cpu(cpu)
*per_cpu_ptr(mmu->last_vcpu_ran, cpu) = -1;
It may be worthy to have comments like below:
/* The eager page splitting is disabled by default */
+ mmu->split_page_cache.gfp_zero = __GFP_ZERO;
+ mmu->split_page_chunk_size = KVM_ARM_EAGER_SPLIT_CHUNK_SIZE_DEFAULT;
+
mmu->pgt = pgt;
mmu->pgd_phys = __pa(pgt->pgd);
return 0;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d77aef872a0a0..f18b48fcd25ba 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1184,6 +1184,8 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
#define KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP 225
#define KVM_CAP_PMU_EVENT_MASKED_EVENTS 226
+#define KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE 227
+#define KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES 228
#ifdef KVM_CAP_IRQ_ROUTING
Thanks,
Gavin
