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[2003:cb:c721:b900:4f34:b2b7:739d:a650]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37189897128sm3241100f8f.81.2024.08.16.02.42.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Aug 2024 02:42:12 -0700 (PDT) Message-ID: <3962fe91-4af1-4a85-80a9-b89826d31274@redhat.com> Date: Fri, 16 Aug 2024 11:42:10 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: x86/kaslr: Expose and use the end of the physical memory address space To: Thomas Gleixner , Alistair Popple Cc: x86@kernel.org, Dan Williams , dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, max8rr8@gmail.com, linux-kernel@vger.kernel.org, jhubbard@nvidia.com, Kees Cook , Andrew Morton , Oscar Salvador , linux-mm@kvack.org References: <20230810100011.14552-1-max8rr8@gmail.com> <87le17yu5y.ffs@tglx> <66b4eb2a62f6_c1448294b0@dwillia2-xfh.jf.intel.com.notmuch> <877ccryor7.ffs@tglx> <66b4f305eb227_c144829443@dwillia2-xfh.jf.intel.com.notmuch> <66b4f4a522508_c1448294f2@dwillia2-xfh.jf.intel.com.notmuch> <87zfpmyhvr.ffs@tglx> <66b523ac448e2_c1448294ec@dwillia2-xfh.jf.intel.com.notmuch> <87seve4e37.fsf@nvdebian.thelocal> <66b59314b3d4_c1448294d3@dwillia2-xfh.jf.intel.com.notmuch> <87zfpks23v.ffs@tglx> <87o75y428z.fsf@nvdebian.thelocal> <87ikw6rrau.ffs@tglx> <87frr9swmw.ffs@tglx> <87bk1x42vk.fsf@nvdebian.thelocal> <87sev8rfyx.ffs@tglx> <87le10p3ak.ffs@tglx> <87ed6soy3z.ffs@tglx> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit > MAX_PHYSMEM_BITS cannot be changed for that because the randomization > does not align with address bit boundaries and there are other places > which actually require to know the maximum number of address bits. All > remaining usage sites of MAX_PHYSMEM_BITS have been analyzed and found > to be correct. > Hi Thomas, > Cure this by exposing the end of the direct map via PHYSMEM_END and use > that for the memory hot-plug and resource management related places > instead of relying on MAX_PHYSMEM_BITS. In the KASLR case PHYSMEM_END > maps to a variable which is initialized by the KASLR initialization and > otherwise it is based on MAX_PHYSMEM_BITS as before. Skimming this patch, I got confused why physmem_end is introduced. I can see a single modification of physmem_end: physmem_end = ((1ULL << MAX_PHYSMEM_BITS) - 1); Which is exactly the same as #ifndef PHYSMEM_END # define PHYSMEM_END ((1ULL << MAX_PHYSMEM_BITS) - 1) #endif And that left me confused why that is required. So we can catch the transition "physmem_end == 0" -> "physmem_end != 0"? I'm probably missing something important, so sorry for the (likely) stupid question. Apart from that, nothing jumped at me. -- Cheers, David / dhildenb