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>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c3afbfe..171bcea 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -135,13 +135,6 @@
#define ACC_USER_MASK PT_USER_MASK
#define ACC_ALL (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
-struct kvm_pv_mmu_op_buffer {
- void *ptr;
- unsigned len;
- unsigned processed;
- char buf[512] __aligned(sizeof(long));
-};
-
struct kvm_rmap_desc {
u64 *shadow_ptes[RMAP_EXT];
struct kvm_rmap_desc *more;
@@ -2292,18 +2285,18 @@
gpa_t addr, unsigned long *ret)
{
int r;
- struct kvm_pv_mmu_op_buffer buffer;
+ struct kvm_pv_mmu_op_buffer *buffer = &vcpu->arch.mmu_op_buffer;
- buffer.ptr = buffer.buf;
- buffer.len = min_t(unsigned long, bytes, sizeof buffer.buf);
- buffer.processed = 0;
+ buffer->ptr = buffer->buf;
+ buffer->len = min_t(unsigned long, bytes, sizeof buffer->buf);
+ buffer->processed = 0;
- r = kvm_read_guest(vcpu->kvm, addr, buffer.buf, buffer.len);
+ r = kvm_read_guest(vcpu->kvm, addr, buffer->buf, buffer->len);
if (r)
goto out;
- while (buffer.len) {
- r = kvm_pv_mmu_op_one(vcpu, &buffer);
+ while (buffer->len) {
+ r = kvm_pv_mmu_op_one(vcpu, buffer);
if (r < 0)
goto out;
if (r == 0)
@@ -2312,7 +2305,7 @@
r = 1;
out:
- *ret = buffer.processed;
+ *ret = buffer->processed;
return r;
}