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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 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 Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: bn6o3f76cji8d6f3cedjhmjjdaeqzwma X-Rspam-User: X-Rspamd-Queue-Id: 799921C0016 X-Rspamd-Server: rspam02 X-HE-Tag: 1723801339-994825 X-HE-Meta: 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 38cVr7LU Onhrxi84iVmjL5YXIBT1ohmT02u3DSJJKbW+PgPYLpVUItoZKYNmMegzPLQhimLzeBMv1pkeYK3A1aHiH2LRTgGKVobbdNTy7b71iK22I4e84ZcWe9ViW1tW+OJLJAB5gK2XBUYxKYJybM67jIfKSlXmZzkUo5uunSebD7TV8PmtkSXNkX5uwUbcINbwNUmi+uGbJBGMKhr6heSO9h4MfQOoCN4qgXkZNsxpj0rlIpe/uhmQX9NDubOhpG76HjXH7q3oyUxvGqmhY0erogOWnB0f11/HB2DGldnUpjiBC03R3uizVLpIQDC0cer2LNs94Y4aFUVb4YusXTO27U7JltfFD7P11XL1zsAimlgL70LBLJs7a3NuWNG0SX9MWLgPahYvOigpkVpy0Y0e6dfHjZxF3ZQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > 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