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[35.233.69.230]) by smtp.gmail.com with ESMTPSA id t18sm8959891wrr.56.2021.02.04.10.01.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 10:01:15 -0800 (PST) Date: Thu, 4 Feb 2021 18:01:12 +0000 From: Quentin Perret To: Will Deacon Cc: Catalin Marinas , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Rob Herring , Frank Rowand , devicetree@vger.kernel.org, android-kvm@google.com, linux-kernel@vger.kernel.org, kernel-team@android.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Fuad Tabba , Mark Rutland , David Brazdil Subject: Re: [RFC PATCH v2 12/26] KVM: arm64: Introduce a Hyp buddy page allocator Message-ID: References: <20210108121524.656872-1-qperret@google.com> <20210108121524.656872-13-qperret@google.com> <20210202181307.GA17311@willie-the-truck> <20210204143106.GA20792@willie-the-truck> <20210204174849.GA21303@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210204174849.GA21303@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Thursday 04 Feb 2021 at 17:48:49 (+0000), Will Deacon wrote: > On Thu, Feb 04, 2021 at 02:52:52PM +0000, Quentin Perret wrote: > > On Thursday 04 Feb 2021 at 14:31:08 (+0000), Will Deacon wrote: > > > On Wed, Feb 03, 2021 at 06:33:30PM +0000, Quentin Perret wrote: > > > > On Tuesday 02 Feb 2021 at 18:13:08 (+0000), Will Deacon wrote: > > > > > On Fri, Jan 08, 2021 at 12:15:10PM +0000, Quentin Perret wrote: > > > > > > + * __find_buddy(pool, page 0, order 0) => page 1 > > > > > > + * __find_buddy(pool, page 0, order 1) => page 2 > > > > > > + * __find_buddy(pool, page 1, order 0) => page 0 > > > > > > + * __find_buddy(pool, page 2, order 0) => page 3 > > > > > > + */ > > > > > > +static struct hyp_page *__find_buddy(struct hyp_pool *pool, struct hyp_page *p, > > > > > > + unsigned int order) > > > > > > +{ > > > > > > + phys_addr_t addr = hyp_page_to_phys(p); > > > > > > + > > > > > > + addr ^= (PAGE_SIZE << order); > > > > > > + if (addr < pool->range_start || addr >= pool->range_end) > > > > > > + return NULL; > > > > > > > > > > Are these range checks only needed because the pool isn't required to be > > > > > an exact power-of-2 pages in size? If so, maybe it would be more > > > > > straightforward to limit the max order on a per-pool basis depending upon > > > > > its size? > > > > > > > > More importantly, it is because pages outside of the pool are not > > > > guaranteed to be covered by the hyp_vmemmap, so I really need to make > > > > sure I don't dereference them. > > > > > > Wouldn't having a per-pool max order help with that? > > > > The issue is, I have no alignment guarantees for the pools, so I may end > > up with max_order = 0 ... > > Yeah, so you would still need the range tracking, Hmm actually I don't think I would, but that would essentially mean the 'buddy' allocator is now turned into a free list of single pages (because we cannot create pages of order 1). > but it would at least help > to reduce HYP_MAX_ORDER failed searches each time. Still, we can always do > that later. Sorry but I am not following. In which case do we have HYP_MAX_ORDER failed searches? Thanks, Quentin