| Message ID | 1432983566-15773-8-git-send-email-guangrong.xiao@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <guangrong.xiao@linux.intel.com> > --- > 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. 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... > + 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. Paolo > + > + /* 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_state->def_type; > } > - > -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); > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 <guangrong.xiao@linux.intel.com> >> --- >> 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 kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 03/06/2015 04:12, Xiao Guangrong wrote: >> >> 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". Choosing MTRR_TYPE_WRTHROUGH is one example of achieve undefined behavior. Picking one type arbitrarily is just a different kind of undefined behavior. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; /* 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)) { + 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_state->def_type; } - -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);
- 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> --- arch/x86/kvm/mtrr.c | 89 ++++++++++++++++++++++++++--------------------------- 1 file changed, 44 insertions(+), 45 deletions(-)