Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752355AbbFAJRG (ORCPT ); Mon, 1 Jun 2015 05:17:06 -0400 Received: from mail-wi0-f181.google.com ([209.85.212.181]:38413 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752113AbbFAJQy (ORCPT ); Mon, 1 Jun 2015 05:16:54 -0400 Message-ID: <556C22FC.50505@redhat.com> Date: Mon, 01 Jun 2015 11:16:44 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Xiao Guangrong CC: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 07/15] KVM: MTRR: improve kvm_mtrr_get_guest_memory_type References: <1432983566-15773-1-git-send-email-guangrong.xiao@linux.intel.com> <1432983566-15773-8-git-send-email-guangrong.xiao@linux.intel.com> In-Reply-To: <1432983566-15773-8-git-send-email-guangrong.xiao@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5595 Lines: 176 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 > --- > 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 linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/