Messages in this thread | | | Subject | Re: [PATCH] X86: don't report PAT on CPUs that don't support it | From | "H. Peter Anvin" <> | Date | Tue, 18 Apr 2017 12:28:20 -0700 |
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On 04/18/17 12:07, Mikulas Patocka wrote: > In the file arch/x86/mm/pat.c, there's a variable __pat_enabled. The > variable is set to 1 by default and the function pat_init() sets > __pat_enabled to 0 if the CPU doesn't support PAT. > > However, on AMD K6-3 CPU, the processor initialization code never calls > pat_init() and so __pat_enabled stays 1 and the function pat_enabled() > returns true, even though the K6-3 CPU doesn't support PAT. > > The result of this bug is that this warning is produced when attemting to > start the Xserver and the Xserver doesn't start (fork() returns ENOMEM). > Another symptom of this bug is that the framebuffer driver doesn't set the > K6-3 MTRR registers. > > This patch changes pat_enabled() so that it returns true only if pat > initialization was actually done. > > Also, I changed boot_cpu_has(X86_FEATURE_PAT) to > this_cpu_has(X86_FEATURE_PAT) in pat_ap_init, so that we check the PAT > feature on the processor that is being initialized. >
I'm thinking it would be better to replace __pat_enabled with static_cpu_has(X86_FEATURE_PAT) and disable the feature bit if the user has disabled it on the command line, just as we do with other features.
-hpa
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