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Shutemov" Cc: Dave Hansen , Andy Lutomirski , x86@kernel.org, Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFCv2 00/10] Linear Address Masking enabling In-Reply-To: <20bada85-9203-57f4-2502-57a6fd11f3ea@intel.com> References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511064943.GR76023@worktop.programming.kicks-ass.net> <20bada85-9203-57f4-2502-57a6fd11f3ea@intel.com> Date: Thu, 12 May 2022 21:39:30 +0200 Message-ID: <875ymav8ul.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 915FB4009F X-Stat-Signature: 1e387tniiupmse8kummdqdr4eiosmq9x Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=linutronix.de header.s=2020 header.b=DLIGD7nk; dkim=pass header.d=linutronix.de header.s=2020e header.b=F2+NdbtV; dmarc=pass (policy=none) header.from=linutronix.de; spf=pass (imf12.hostedemail.com: domain of tglx@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=tglx@linutronix.de X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1652384349-826891 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: On Thu, May 12 2022 at 10:22, Dave Hansen wrote: > On 5/10/22 23:49, Peter Zijlstra wrote: >>> The feature competes for bits with 5-level paging: LAM_U48 makes it >>> impossible to map anything about 47-bits. The patchset made these >>> capability mutually exclusive: whatever used first wins. LAM_U57 can be >>> combined with mappings above 47-bits. >> So aren't we creating a problem with LAM_U48 where programs relying on >> it are of limited sustainability? > > I think allowing apps to say, "It's LAM_U48 or bust!" is a mistake. That'd be outright stupid. > It's OK for a debugging build that runs on one kind of hardware. But, > if we want LAM-using binaries to be portable, we have to do something > different. > > One of the stated reasons for adding LAM hardware is that folks want to > use sanitizers outside of debugging environments. To me, that means > that LAM is something that the same binary might run with or without. On/off yes, but is there an actual use case where such a mechanism would at start time dynamically chose the number of bits? > It's totally fine with me if the kernel only initially supports LAM_U57. > But, I'd ideally like to make sure that the ABI can support LAM_U57, > LAM_U48, AMD's UAI (in whatever form it settles), or other masks. Sure. No argument here. Thanks, tglx