On Tue, Jun 6, 2017 at 3:49 PM, Mikulas Patocka <[email protected]> wrote: > > > On Sun, 28 May 2017, Andy Lutomirski wrote: > >> On Sun, May 28, 2017 at 11:18 AM, Bernhard Held <[email protected]> wrote: >> > Hi, >> > >> > this patch breaks the boot of my kernel. The last message is "Booting >> > the kernel.". >> > >> > My setup might be unusual: I'm running a Xenon E5450 (LGA 771) in a >> > Gigbayte G33-DS3R board (LGA 775). The BIOS is patched with the >> > microcode of the E5450 and recognizes the CPU. >> > >> > Please find below the dmesg of a the latest kernel w/o the PAT-patch. >> > I'm happy to provide more information or to test patches. >> >> I think this patch is bogus. pat_enabled() sure looks like it's >> supposed to return true if PAT is *enabled*, and these days PAT is >> "enabled" even if there's no HW PAT support. Even if the patch were >> somehow correct, it should have been split up into two patches, one to >> change pat_enabled() and one to use this_cpu_has(). >> >> Ingo, I'd suggest reverting the patch, cc-ing stable on the revert so >> -stable knows not to backport it, and starting over with the fix. >> >From very brief inspection, the right fix is to make sure that >> pat_init(), or at least init_cache_modes(), gets called on the >> affected CPUs. >> >> --Andy > > Hi > > Here I send the second version of the patch. It drops the change from > boot_cpu_has(X86_FEATURE_PAT) to this_cpu_has(X86_FEATURE_PAT) (that > caused kernel to be unbootable for some people). > > Another change is that setup_arch() calls init_cache_modes() if PAT is > disabled, so that init_cache_modes() is always called. > > Mikulas > > > > From: Mikulas Patocka <[email protected]> > > 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.
Why? Shouldn't calling init_cache_modes() be sufficient? --Andy
