Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753192AbaKCTLc (ORCPT ); Mon, 3 Nov 2014 14:11:32 -0500 Received: from g2t2353.austin.hp.com ([15.217.128.52]:29315 "EHLO g2t2353.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752128AbaKCTL3 (ORCPT ); Mon, 3 Nov 2014 14:11:29 -0500 X-Greylist: delayed 3362 seconds by postgrey-1.27 at vger.kernel.org; Mon, 03 Nov 2014 14:11:29 EST Message-ID: <1415041049.10958.15.camel@misato.fc.hp.com> Subject: Re: [PATCH v4 2/7] x86, mm, pat: Change reserve_memtype() to handle WT From: Toshi Kani To: Thomas Gleixner Cc: hpa@zytor.com, mingo@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgross@suse.com, stefan.bader@canonical.com, luto@amacapital.net, hmh@hmh.eng.br, yigal@plexistor.com, konrad.wilk@oracle.com Date: Mon, 03 Nov 2014 11:57:29 -0700 In-Reply-To: References: <1414450545-14028-1-git-send-email-toshi.kani@hp.com> <1414450545-14028-3-git-send-email-toshi.kani@hp.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4 (3.10.4-4.fc20) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2014-11-03 at 19:27 +0100, Thomas Gleixner wrote: > On Mon, 27 Oct 2014, Toshi Kani wrote: > > This patch changes reserve_memtype() to handle the WT cache mode. > > When PAT is not enabled, it continues to set UC- to *new_type for > > any non-WB request. > > > > When a target range is RAM, reserve_ram_pages_type() fails for WT > > for now. This function may not reserve a RAM range for WT since > > reserve_ram_pages_type() uses the page flags limited to three memory > > types, WB, WC and UC. > > > > Signed-off-by: Toshi Kani > > Reviewed-by: Konrad Rzeszutek Wilk > > --- > > arch/x86/include/asm/cacheflush.h | 4 ++++ > > arch/x86/mm/pat.c | 16 +++++++++++++--- > > 2 files changed, 17 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h > > index 157644b..c912680 100644 > > --- a/arch/x86/include/asm/cacheflush.h > > +++ b/arch/x86/include/asm/cacheflush.h > > @@ -53,6 +53,10 @@ static inline void set_page_memtype(struct page *pg, > > case _PAGE_CACHE_MODE_WB: > > memtype_flags = _PGMT_WB; > > break; > > + case _PAGE_CACHE_MODE_WT: > > + case _PAGE_CACHE_MODE_WP: > > + pr_err("set_page_memtype: unsupported cachemode %d\n", memtype); > > + BUG(); > > You already catch the cases with the hunk below at the entry of > reserve_ram_pages_type(). So what's the point of the BUG()? > > If you are worried about other usage sites: This function should not > at all be in arch/x86/include/asm/cacheflush.h. It's solely used by > PAT, so we really should move it there before changing it. Yes, I was worried about other usage. I agree that this function should belong to PAT. I will move it to pat.c before changing it, and will remove BUG() from this patch. > > default: > > memtype_flags = _PGMT_DEFAULT; > > break; > > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c > > index db687c3..a214f5a 100644 > > --- a/arch/x86/mm/pat.c > > +++ b/arch/x86/mm/pat.c > > @@ -289,6 +289,8 @@ static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end) > > > > /* > > * For RAM pages, we use page flags to mark the pages with appropriate type. > > + * The page flags are currently limited to three types, WB, WC and UC. Hence, > > + * any request to WT or WP will fail with -EINVAL. > > * Here we do two pass: > > * - Find the memtype of all the pages in the range, look for any conflicts > > * - In case of no conflicts, set the new memtype for pages in the range > > @@ -300,6 +302,13 @@ static int reserve_ram_pages_type(u64 start, u64 end, > > struct page *page; > > u64 pfn; > > > > + if ((req_type == _PAGE_CACHE_MODE_WT) || > > + (req_type == _PAGE_CACHE_MODE_WP)) { > > + if (new_type) > > + *new_type = _PAGE_CACHE_MODE_UC_MINUS; > > + return -EINVAL; > > + } > > + > > if (req_type == _PAGE_CACHE_MODE_UC) { > > /* We do not support strong UC */ > > WARN_ON_ONCE(1); > > @@ -349,6 +358,7 @@ static int free_ram_pages_type(u64 start, u64 end) > > * - _PAGE_CACHE_MODE_WC > > * - _PAGE_CACHE_MODE_UC_MINUS > > * - _PAGE_CACHE_MODE_UC > > + * - _PAGE_CACHE_MODE_WT > > * > > * If new_type is NULL, function will return an error if it cannot reserve the > > * region with req_type. If new_type is non-NULL, function will return > > @@ -368,10 +378,10 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type, > > if (!pat_enabled) { > > /* This is identical to page table setting without PAT */ > > if (new_type) { > > - if (req_type == _PAGE_CACHE_MODE_WC) > > - *new_type = _PAGE_CACHE_MODE_UC_MINUS; > > + if (req_type == _PAGE_CACHE_MODE_WB) > > + *new_type = _PAGE_CACHE_MODE_WB; > > else > > - *new_type = req_type; > > + *new_type = _PAGE_CACHE_MODE_UC_MINUS; > > So until now we supported WB, UC- and UC and mapped WC to UC-. Now we > map everything except WB to UC- > Why feels that wrong without a comment explaining it? The case of !pat_enable only supports WB and UC-. Previously, WC was the only type that needed to be mapped to UC-. The code now handles it properly for any other types. Yes, I will add a comment for this. Thanks, -Toshi -- 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/