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Commit 6ad18fba authored by Dave Hansen's avatar Dave Hansen Committed by Avi Kivity
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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: default avatarDave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent b772ff36

arch/x86/kvm/mmu.c

+8 −15
Original line number Diff line number Diff line
@@ -135,13 +135,6 @@ module_param(dbg, bool, 0644); 
#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 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes, 
		  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 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes, 


	r = 1;

out:

	*ret = buffer.processed;

	*ret = buffer->processed;

	return r;

}

include/asm-x86/kvm_host.h

+10 −0
Original line number Diff line number Diff line
@@ -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;