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Tue, 13 Oct 2026 19:51:15 +0000 Message-ID: Date: Tue, 13 Oct 2026 12:51:12 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] selftests/x86: Add a test for LASS enforcement Content-Language: en-US To: "H. Peter Anvin" , , Borislav Petkov , Dave Hansen CC: Thomas Gleixner , Ingo Molnar , "Shuah Khan" , Binbin Wu , "Peter Zijlstra" , "Chang S . 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Peter Anvin wrote: > On 2026-10-08 19:00, Sohil Mehta wrote: >> >> Note, the CPUID bit does not reflect whether the kernel enabled LASS; >> only the cpuinfo flag does. But parsing cpuinfo is cumbersome, and the >> kernel enables LASS whenever the CPU supports it unless the command line >> opts out (vsyscall=emulate or clearcpuid=lass). To keep it simple, rely >> on the CPUID bit and accept a failure in these unusual cases. >> > Cumbersome, really? > I had it in v1 of this patch. It seemed excessive to do specifically for LASS: https://lore.kernel.org/lkml/20260806011536.4172258-8-sohil.mehta@intel.com/ As LASS is always enabled by the kernel except for the really odd cases the trade-off seems practical to me. > Here is a set of parsing functions -- tested, even! -- that you can make > available as library routines. Integrating them into the selftests build > framework has been left as an exercise for the reader ;-) > I agree, adding them as generic selftest helpers may be useful. But, /proc/cpuinfo has been unreliable in general. It is currently buggy for some features with Kconfig options. See: https://lore.kernel.org/lkml/f6f113b46199d996c4f81fc89858c2f484256418.1774623092.git.m.wieczorretman@pm.me/ Also, (I think) we have been generally discouraging folks to add more bits there. So, I don't know if creating these library routines is useful right now. IIUC, Boris said that the CPUID rework would make some of cpuinfo stuff moot. https://lore.kernel.org/lkml/20260331140216.GDacvT6IPW1gf003z-@fat_crate.local/ Thoughts?