From 3f3f78b61462fdc62469334c259b1e5555ebd1ed Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Mon, 15 Jun 2015 16:55:28 +0800 Subject: 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: Xiao Guangrong Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mtrr.c | 94 ++++++++++++++++++++++++++++------------------------- 1 file changed, 49 insertions(+), 45 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c index c4b80a46a530..2ea12130e74a 100644 --- a/arch/x86/kvm/mtrr.c +++ b/arch/x86/kvm/mtrr.c @@ -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); -- cgit v1.2.3