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Commit 3f3f78b6 authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Paolo Bonzini
Browse files

KVM: MTRR: improve kvm_mtrr_get_guest_memory_type 



 - kvm_mtrr_get_guest_memory_type() only checks one page in MTRRs so
   that it's unnecessary to check to see if the range is partially
   covered in MTRR

 - optimize the check of overlap memory type and add some comments
   to explain the precedence

Signed-off-by: default avatarXiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 86fd5270

arch/x86/kvm/mtrr.c

+49 −45
Original line number Diff line number Diff line
@@ -249,24 +249,22 @@ int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata) 
	return 0;

}



/*

 * The function is based on mtrr_type_lookup() in

 * arch/x86/kernel/cpu/mtrr/generic.c

 */

static int get_mtrr_type(struct kvm_mtrr *mtrr_state,

			 u64 start, u64 end)

u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)

{

	u64 base, mask;

	u8 prev_match, curr_match;

	int i, num_var_ranges = KVM_NR_VAR_MTRR;

	struct kvm_mtrr *mtrr_state = &vcpu->arch.mtrr_state;

	u64 base, mask, start;

	int i, num_var_ranges, type;

	const int wt_wb_mask = (1 << MTRR_TYPE_WRBACK)

			       | (1 << MTRR_TYPE_WRTHROUGH);



	start = gfn_to_gpa(gfn);

	num_var_ranges = KVM_NR_VAR_MTRR;

	type = -1;



	/* MTRR is completely disabled, use UC for all of physical memory. */

	if (!mtrr_is_enabled(mtrr_state))

		return MTRR_TYPE_UNCACHABLE;



	/* Make end inclusive end, instead of exclusive */

	end--;



	/* Look in fixed ranges. Just return the type as per start */

	if (fixed_mtrr_is_enabled(mtrr_state) && (start < 0x100000)) {

		int idx;
@@ -291,9 +289,8 @@ static int get_mtrr_type(struct kvm_mtrr *mtrr_state, 
	 * Look of multiple ranges matching this address and pick type

	 * as per MTRR precedence

	 */

	prev_match = 0xFF;

	for (i = 0; i < num_var_ranges; ++i) {

		unsigned short start_state, end_state;

		int curr_type;



		if (!(mtrr_state->var_ranges[i].mask & (1 << 11)))

			continue;
@@ -301,50 +298,57 @@ static int get_mtrr_type(struct kvm_mtrr *mtrr_state, 
		base = mtrr_state->var_ranges[i].base & PAGE_MASK;

		mask = mtrr_state->var_ranges[i].mask & PAGE_MASK;



		start_state = ((start & mask) == (base & mask));

		end_state = ((end & mask) == (base & mask));

		if (start_state != end_state)

			return 0xFE;



		if ((start & mask) != (base & mask))

			continue;



		curr_match = mtrr_state->var_ranges[i].base & 0xff;

		if (prev_match == 0xFF) {

			prev_match = curr_match;

		/*

		 * Please refer to Intel SDM Volume 3: 11.11.4.1 MTRR

		 * Precedences.

		 */



		curr_type = mtrr_state->var_ranges[i].base & 0xff;

		if (type == -1) {

			type = curr_type;

			continue;

		}



		if (prev_match == MTRR_TYPE_UNCACHABLE ||

		    curr_match == MTRR_TYPE_UNCACHABLE)

			return MTRR_TYPE_UNCACHABLE;



		if ((prev_match == MTRR_TYPE_WRBACK &&

		     curr_match == MTRR_TYPE_WRTHROUGH) ||

		    (prev_match == MTRR_TYPE_WRTHROUGH &&

		     curr_match == MTRR_TYPE_WRBACK)) {

			prev_match = MTRR_TYPE_WRTHROUGH;

			curr_match = MTRR_TYPE_WRTHROUGH;

		}

		/*

		 * If two or more variable memory ranges match and the

		 * memory types are identical, then that memory type is

		 * used.

		 */

		if (type == curr_type)

			continue;



		if (prev_match != curr_match)

		/*

		 * If two or more variable memory ranges match and one of

		 * the memory types is UC, the UC memory type used.

		 */

		if (curr_type == MTRR_TYPE_UNCACHABLE)

			return MTRR_TYPE_UNCACHABLE;



		/*

		 * If two or more variable memory ranges match and the

		 * memory types are WT and WB, the WT memory type is used.

		 */

		if (((1 << type) & wt_wb_mask) &&

		      ((1 << curr_type) & wt_wb_mask)) {

			type = MTRR_TYPE_WRTHROUGH;

			continue;

		}



	if (prev_match != 0xFF)

		return prev_match;

		/*

		 * For overlaps not defined by the above rules, processor

		 * behavior is undefined.

		 */



	return mtrr_default_type(mtrr_state);

		/* We use WB for this undefined behavior. :( */

		return MTRR_TYPE_WRBACK;

	}



u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)

{

	u8 mtrr;

	if (type != -1)

		return type;



	mtrr = get_mtrr_type(&vcpu->arch.mtrr_state, gfn << PAGE_SHIFT,

			     (gfn << PAGE_SHIFT) + PAGE_SIZE);

	if (mtrr == 0xfe || mtrr == 0xff)

		mtrr = MTRR_TYPE_WRBACK;

	return mtrr;

	return mtrr_default_type(mtrr_state);

}

EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);