On 06/01/2015 05:16 PM, Paolo Bonzini wrote:
On 30/05/2015 12:59, Xiao Guangrong wrote:- 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 <[email protected]> --- arch/x86/kvm/mtrr.c | 89 ++++++++++++++++++++++++++--------------------------- 1 file changed, 44 insertions(+), 45 deletions(-) diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c index bc9c6da..d3c06d2 100644 --- a/arch/x86/kvm/mtrr.c +++ b/arch/x86/kvm/mtrr.c @@ -231,24 +231,16 @@ 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 = gfn_to_gpa(gfn); + int i, num_var_ranges = KVM_NR_VAR_MTRR, type_mask, type = -1;Do not mix initialized and uninitialized variables on the same line (preexisting, I know, but let's fix it instead of making it worse :)). Please put each initialized variable on a separate line.
Okay. Will follow this style in the future development.
Also please initialize type_mask here (more on this below)./* MTRR is completely disabled, use UC for all of physical memory. */ if (!mtrr_state->mtrr_enabled) return MTRR_TYPE_UNCACHABLE; - /* Make end inclusive end, instead of exclusive */ - end--; - /* Look in fixed ranges. Just return the type as per start */ if (mtrr_state->fixed_mtrr_enabled && (start < 0x100000)) { int idx; @@ -273,9 +265,9 @@ 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; + type_mask = (1 << MTRR_TYPE_WRBACK) | (1 << MTRR_TYPE_WRTHROUGH); 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; @@ -283,50 +275,57 @@ 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) & type_mask) && + ((1 << curr_type) & type_mask)) {Please inline definition of type_mask in the "if", or rename it to "wt_wb_mask" and make it const. Or another suggestion below...
Okay, it's a better name indeed.
+ 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. + */Perhaps just use type = MIN(type, curr_type), which also happens to get WT vs. WB right? You can also add a BUILD_BUG_ON(MTRR_TYPE_WRTHROUGH > MTRR_TYPE_WRBACK); to ensure that the WT vs. WB precedence is correct.
Only WT and WB are allowed to be overlapped here otherwise is "undefined behavior". For example if the types are MTRR_TYPE_WRPROT and MTRR_TYPE_WRTHROUGH, min() will get MTRR_TYPE_WRTHROUGH rather than "undefined behavior". -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
