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Peter Anvin" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/13] arm64: mm: Add p?d_large() definitions Message-ID: <20190218134507.GA9603@lakrids.cambridge.arm.com> References: <20190215170235.23360-1-steven.price@arm.com> <20190215170235.23360-2-steven.price@arm.com> <20190218112922.GT32477@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190218112922.GT32477@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 18, 2019 at 12:29:22PM +0100, Peter Zijlstra wrote: > On Fri, Feb 15, 2019 at 05:02:22PM +0000, Steven Price wrote: > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index de70c1eabf33..09d308921625 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -428,6 +428,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, > > PMD_TYPE_TABLE) > > #define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \ > > PMD_TYPE_SECT) > > +#define pmd_large(x) pmd_sect(x) > > > > #if defined(CONFIG_ARM64_64K_PAGES) || CONFIG_PGTABLE_LEVELS < 3 > > #define pud_sect(pud) (0) > > @@ -435,6 +436,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, > > #else > > #define pud_sect(pud) ((pud_val(pud) & PUD_TYPE_MASK) == \ > > PUD_TYPE_SECT) > > +#define pud_large(x) pud_sect(x) > > #define pud_table(pud) ((pud_val(pud) & PUD_TYPE_MASK) == \ > > PUD_TYPE_TABLE) > > #endif > > So on x86 p*d_large() also matches p*d_huge() and thp, But it is not > clear to me this p*d_sect() thing does so, given your definitions. > > See here why I care: > > http://lkml.kernel.org/r/20190201124741.GE31552@hirez.programming.kicks-ass.net I believe it does not. IIUC our p?d_huge() helpers implicitly handle contiguous entries. That's where you have $N entries in the current level of table that the TLB can cache together as one. Our p?d_sect() helpers only match section entries. That's where we map an entire next-level-table's worth of VA space with a single entry at the current level. Thanks, Mark.