KVM: arm64: Add KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE

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@linux.dev>
Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Link: https://lore.kernel.org/r/20230426172330.1439644-6-ricarkol@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7e7e19ef6993..b743198450b3 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -159,6 +159,21 @@ 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. The choice of KVM_CAP_ARM_EAGER_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;
 };