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KVM: MTRR: improve kvm_mtrr_get_guest_memory_type

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- 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: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Xiao Guangrong 2015-06-15 16:55:28 +08:00 committed by Paolo Bonzini
parent 86fd52701c
commit 3f3f78b614
1 changed files with 49 additions and 45 deletions
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94
arch/x86/kvm/mtrr.c
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@ -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)
/*
* 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 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 ((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 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 != curr_match)
return MTRR_TYPE_UNCACHABLE;
/*
* For overlaps not defined by the above rules, processor
* behavior is undefined.
*/
/* We use WB for this undefined behavior. :( */
return MTRR_TYPE_WRBACK;
}
if (prev_match != 0xFF)
return prev_match;
if (type != -1)
return type;
return mtrr_default_type(mtrr_state);
}
u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
{
u8 mtrr;
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;
}
EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);