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AJvYcCXfFkoUTsqNQZE2JQs3hv3EpGeFSIxcTWvTXA4FX1JULooBQJfn4ZoZA/Z1W4UjbnEAr14SmQRcC8Mg6pY=@vger.kernel.org X-Gm-Message-State: AOJu0YyF0w0xzk14JNO4NEToE4JSkWHwpbM4bFwKoOc4PYq6573ft+Ey pKRif3oj1I3XOsVcn6GSAzJOL9mdNMZPm/R11YTl2afltzPqZ8MonVuuvl/21yroi25Ijg9Tb+Q PFXOEXVjbd/0D4vAQTA== X-Google-Smtp-Source: AGHT+IFO60SlOVXFGfc/szhJVpc75spqpNw2IzzXevlhy4U/0PpbLpo4ep7Q2sEdRzo+JtTGmKQPtisVnvfyVrfn X-Received: from plbkv16.prod.google.com ([2002:a17:903:28d0:b0:227:e456:d436]) (user=changyuanl job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:cf04:b0:220:bd61:a337 with SMTP id d9443c01a7336-22bea4c62b2mr18031945ad.23.1744344150948; Thu, 10 Apr 2025 21:02:30 -0700 (PDT) Date: Thu, 10 Apr 2025 21:02:07 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.49.0.604.gff1f9ca942-goog Message-ID: <20250411040207.1785245-1-changyuanl@google.com> Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation From: Changyuan Lyu To: ptyadav@amazon.de Cc: akpm@linux-foundation.org, anthony.yznaga@oracle.com, arnd@arndb.de, ashish.kalra@amd.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, changyuanl@google.com, corbet@lwn.net, dave.hansen@linux.intel.com, devicetree@vger.kernel.org, dwmw2@infradead.org, ebiederm@xmission.com, graf@amazon.com, hpa@zytor.com, jgg@nvidia.com, jgowans@amazon.com, kexec@lists.infradead.org, krzk@kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, luto@kernel.org, mark.rutland@arm.com, mingo@redhat.com, pasha.tatashin@soleen.com, pbonzini@redhat.com, peterz@infradead.org, robh+dt@kernel.org, robh@kernel.org, rostedt@goodmis.org, rppt@kernel.org, saravanak@google.com, skinsburskii@linux.microsoft.com, tglx@linutronix.de, thomas.lendacky@amd.com, will@kernel.org, x86@kernel.org Content-Type: text/plain; charset="UTF-8" Hi Pratyush, Thanks for reviewing! On Wed, Apr 02, 2025 at 19:16:27 +0000, Pratyush Yadav wrote: > Hi Changyuan, > > On Wed, Mar 19 2025, Changyuan Lyu wrote: > > [...] > > +int kho_preserve_phys(phys_addr_t phys, size_t size) > > +{ > > + unsigned long pfn = PHYS_PFN(phys), end_pfn = PHYS_PFN(phys + size); > > + unsigned int order = ilog2(end_pfn - pfn); > > This caught my eye when playing around with the code. It does not put > any limit on the order, so it can exceed NR_PAGE_ORDERS. I agree with Mike that this should not be a problem. > Also, when > initializing the page after KHO, we pass the order directly to > prep_compound_page() without sanity checking it. The next kernel might > not support all the orders the current one supports. Perhaps something > to fix? Yes the new kernel should check the order. > > + unsigned long failed_pfn; > > + int err = 0; > > + > > + if (!kho_enable) > > + return -EOPNOTSUPP; > > + > > + down_read(&kho_out.tree_lock); > > + if (kho_out.fdt) { > > + err = -EBUSY; > > + goto unlock; > > + } > > + > > + for (; pfn < end_pfn; > > + pfn += (1 << order), order = ilog2(end_pfn - pfn)) { > > + err = __kho_preserve(&kho_mem_track, pfn, order); I realized another bug here: we did not check if "pfn" is aligned to 1 << order. For example, if the function input is @phys = 4096, @size = 8192, in the 1st iteration, pfn = 1, end_pfn = 3, order = 1. This is problematic since these 2 pages should be viewed as 2 folios of order 0, instead of 1 folio of order 1. > > + if (err) { > > + failed_pfn = pfn; > > + break; > > + } > > + } > [...] I will fix the 2 bugs above in V6. Best, Changyuan