KVM: Reduce stack usage in kvm_pv_mmu_op()

We're in a hot path.  We can't use kmalloc() because
it might impact performance.  So, we just stick the buffer that
we need into the kvm_vcpu_arch structure.  This is used very
often, so it is not really a waste.

We also have to move the buffer structure's definition to the
arch-specific x86 kvm header.

Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 99dddfc..9cb4b4d 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -201,6 +201,13 @@ struct kvm_mmu_page {
 	};
 };
 
+struct kvm_pv_mmu_op_buffer {
+	void *ptr;
+	unsigned len;
+	unsigned processed;
+	char buf[512] __aligned(sizeof(long));
+};
+
 /*
  * x86 supports 3 paging modes (4-level 64-bit, 3-level 64-bit, and 2-level
  * 32-bit).  The kvm_mmu structure abstracts the details of the current mmu
@@ -248,6 +255,9 @@ struct kvm_vcpu_arch {
 	bool tpr_access_reporting;
 
 	struct kvm_mmu mmu;
+	/* only needed in kvm_pv_mmu_op() path, but it's hot so
+	 * put it here to avoid allocation */
+	struct kvm_pv_mmu_op_buffer mmu_op_buffer;
 
 	struct kvm_mmu_memory_cache mmu_pte_chain_cache;
 	struct kvm_mmu_memory_cache mmu_rmap_desc_cache;