From cbed27cdf0e3f7ea3b2259e86b9e34df02be3fe4 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 18 Apr 2017 15:07:11 -0400 Subject: x86/PAT: Fix Xorg regression on CPUs that don't support PAT In the file arch/x86/mm/pat.c, there's a '__pat_enabled' variable. 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 CPUs, 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 a kernel warning is produced when attempting 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: x86/PAT: Xorg:3891 map pfn expected mapping type uncached-minus for [mem 0xe4000000-0xe5ffffff], got write-combining ------------[ cut here ]------------ WARNING: CPU: 0 PID: 3891 at arch/x86/mm/pat.c:1020 untrack_pfn+0x5c/0x9f ... x86/PAT: Xorg:3891 map pfn expected mapping type uncached-minus for [mem 0xe4000000-0xe5ffffff], got write-combining To fix the bug change 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. Signed-off-by: Mikulas Patocka Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Luis R. Rodriguez Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Toshi Kani Cc: stable@vger.kernel.org # v4.2+ Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1704181501450.26399@file01.intranet.prod.int.rdu2.redhat.com Signed-off-by: Ingo Molnar --- arch/x86/mm/pat.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c index 9b78685b66e6..83a59a67757a 100644 --- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -65,9 +65,11 @@ static int __init nopat(char *str) } early_param("nopat", nopat); +static bool __read_mostly __pat_initialized = false; + bool pat_enabled(void) { - return !!__pat_enabled; + return __pat_initialized; } EXPORT_SYMBOL_GPL(pat_enabled); @@ -225,13 +227,14 @@ static void pat_bsp_init(u64 pat) } wrmsrl(MSR_IA32_CR_PAT, pat); + __pat_initialized = true; __init_cache_modes(pat); } static void pat_ap_init(u64 pat) { - if (!boot_cpu_has(X86_FEATURE_PAT)) { + if (!this_cpu_has(X86_FEATURE_PAT)) { /* * If this happens we are on a secondary CPU, but switched to * PAT on the boot CPU. We have no way to undo PAT. @@ -306,7 +309,7 @@ void pat_init(void) u64 pat; struct cpuinfo_x86 *c = &boot_cpu_data; - if (!pat_enabled()) { + if (!__pat_enabled) { init_cache_modes(); return; } -- cgit v1.2.3