| Message ID | trinity-1045dd8c-e43f-4f8c-94e4-c0f0f15f611d-1385507362267@3capp-webde-bs36 |
|---|---|
| State | New |
| Headers | show |
On 11/26/2013 03:09 PM, Roland Kletzing wrote: > Hello kernel-team, > > regarding https://bugs.launchpad.net/ubuntu/+source/syslinux/+bug/930447 , i have developed a simple patch to (hopefully) provide an easy and elegant workaround/fix for the issue. I assume some hundred users (if not some thousand, as entries in bugreports are only the tip of an iceberg) are affected by this issue. > > Please take a review and feel free to merge. > > As defaulting to PAE kernels is specific for some distros only, i think this is no patch for mainline (yet). > > I did not often do patches, nor am i a good programmer - so sorry if the patch or the submission style is not perfect. > > regards > Roland No, this is not an acceptable patch per se. The right way to do this is to have the option, if it is found, simply set the bit in the CPU array. However, it is important to verify that we are on the affected type of CPU, specifically the affected Pentium Ms. x86 patches should be sent to <x86@kernel.org> or equivalently myself, <mingo@kernel.org> and <tglx@linutronix.de> and Cc: <linux-kernel@vger.kernel.org>. I also encourage you to read the file Documentation/SubmittingPatches before trying again. -hpa
This patch is meant primarly for ubuntu, as they only ship PAE enabled kernels and don`t ship non-PAE kernels anymore. So this resolves an ubuntu specific problem (as the installer disc also has PAE enabled kernel). I know it`s not perfect, but poking cpu bits in arrays is above my skills and i have already spent really much time with this trying to resolve a problem for the end-user intruduced by nothing but the decision to discontinue Non-PAE kernels. If grub2 can do nasty or ugly things like skipping standard x86 bootcode (which also skips validate_cpu() - while nobody seems to have a problem with that) , then i don`t understand what´s the real problem to add a very simple and unintrusive quirk to a vendor specific kernel. Let time go by and the quirk will be obsolete one day anyway as no hardware lives forever. But for now there exist distros like lubuntu meant for older hardware, and if installing that on a Pentium M 1,7 Ghz fails because of that nasty PAE issue nobody is willing to fix elegantly, then i think it deserves only one term: planned obsolescence I`s bad enough, that industry does produce products with limited lifetime. Products that break and that even can`t be repaired. So please, kernel people, don`t think that way. Care for the users. Many thinkpad users will be thankful if they can install their favourite distro by just adding a bootparam instead of reading through tons of pages how to add even weirder workarounds like bind-mounting a modified copy of itself on top of /proc/cpuinfo. regards Roland ps: https://help.ubuntu.com/community/Lubuntu-fake-PAE -------------------------------------------------- From: "H. Peter Anvin" <hpa@zytor.com> Sent: Wednesday, November 27, 2013 12:33 AM To: "Roland Kletzing" <devzero@web.de>; <kernel-team@lists.ubuntu.com> Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] - add "fixpae" bootparam to fix/workaround #930447 > On 11/26/2013 03:09 PM, Roland Kletzing wrote: >> Hello kernel-team, >> >> regarding https://bugs.launchpad.net/ubuntu/+source/syslinux/+bug/930447 >> , i have developed a simple patch to (hopefully) provide an easy and >> elegant workaround/fix for the issue. I assume some hundred users (if not >> some thousand, as entries in bugreports are only the tip of an iceberg) >> are affected by this issue. >> >> Please take a review and feel free to merge. >> >> As defaulting to PAE kernels is specific for some distros only, i think >> this is no patch for mainline (yet). >> >> I did not often do patches, nor am i a good programmer - so sorry if the >> patch or the submission style is not perfect. >> >> regards >> Roland > > No, this is not an acceptable patch per se. > > The right way to do this is to have the option, if it is found, simply > set the bit in the CPU array. However, it is important to verify that > we are on the affected type of CPU, specifically the affected Pentium Ms. > > x86 patches should be sent to <x86@kernel.org> or equivalently myself, > <mingo@kernel.org> and <tglx@linutronix.de> and Cc: > <linux-kernel@vger.kernel.org>. I also encourage you to read the file > Documentation/SubmittingPatches before trying again. > > -hpa >
On Wed, Nov 27, 2013 at 09:41:03PM +0100, Roland wrote: > This patch is meant primarly for ubuntu, as they only ship PAE > enabled kernels and don`t ship non-PAE kernels anymore. So this > resolves an ubuntu specific problem (as the installer disc also has > PAE enabled kernel). > > I know it`s not perfect, but poking cpu bits in arrays is above my > skills and i have already spent really much time with this trying to > resolve a problem for the end-user intruduced by nothing but the > decision to discontinue Non-PAE kernels. I think the complaints are more about how it works that the intent. Kernel engineers are by their very nature very risk averse, so it would indeed be good to set the bit correctly in the cpu capability flags, and to do that based on the machine type. I might just have a machine which exhibits this behaviour, I will try and look it out and see if we can morph this into something appropriate. -apw
diff -uprN linux-source-3.11.0.orig/arch/x86/boot/main.c linux-source-3.11.0/arch/x86/boot/main.c --- linux-source-3.11.0.orig/arch/x86/boot/main.c 2013-09-02 22:46:10.000000000 +0200 +++ linux-source-3.11.0/arch/x86/boot/main.c 2013-11-26 20:56:01.175269235 +0100 @@ -146,9 +146,17 @@ void main(void) /* Make sure we have all the proper CPU support */ if (validate_cpu()) { - puts("Unable to boot - please use a kernel appropriate " - "for your CPU.\n"); - die(); + if(cmdline_find_option_bool("fixpae")) + puts("fixpae bootparam active. Skipping CPU " + "validation and continuing Kernel execution\n"); + else { + puts("Unable to boot - please use a kernel appropriate " + "for your CPU.\n" + "Hint: CPU`s like Pentium M may incorrectly report " + "on PAE incapability, so you may try booting with " + "fixpae bootparam as a workaround.\n"); + die(); + } } /* Tell the BIOS what CPU mode we intend to run in. */ diff -uprN linux-source-3.11.0.orig/arch/x86/kernel/cpu/proc.c linux-source-3.11.0/arch/x86/kernel/cpu/proc.c --- linux-source-3.11.0.orig/arch/x86/kernel/cpu/proc.c 2013-09-02 22:46:10.000000000 +0200 +++ linux-source-3.11.0/arch/x86/kernel/cpu/proc.c 2013-11-26 21:15:53.961267903 +0100 @@ -4,6 +4,17 @@ #include <linux/seq_file.h> #include <linux/cpufreq.h> +/* fixpae kernelparam workaround, see kernel-parameters.txt */ +static int fixpaeflag = 0; + +static int __init fixpae(char *s) +{ + fixpaeflag=1; + return 1; +} + +__setup("fixpae", fixpae); + /* * Get CPU information for use by the procfs. */ @@ -96,6 +107,8 @@ static int show_cpuinfo(struct seq_file show_cpuinfo_misc(m, c); seq_printf(m, "flags\t\t:"); + if(fixpaeflag) + seq_printf(m, " pae"); for (i = 0; i < 32*NCAPINTS; i++) if (cpu_has(c, i) && x86_cap_flags[i] != NULL) seq_printf(m, " %s", x86_cap_flags[i]); diff -uprN linux-source-3.11.0.orig/Documentation/kernel-parameters.txt linux-source-3.11.0/Documentation/kernel-parameters.txt --- linux-source-3.11.0.orig/Documentation/kernel-parameters.txt 2013-10-23 19:26:00.000000000 +0200 +++ linux-source-3.11.0/Documentation/kernel-parameters.txt 2013-11-26 21:13:28.515313678 +0100 @@ -900,6 +900,14 @@ bytes respectively. Such letter suffixes Format: <interval>,<probability>,<space>,<times> See also Documentation/fault-injection/. + fixpae [x86] Workaround for a nasty PAE issue with older CPU`s + like Pentium M, as they may report PAE incapability + although they support it. This bootparam adds a fake + pae entry to the flags section in /proc/cpuinfo and + skips the validate_cpu() routine in arch/x86/boot/main.c + This is necesssary as major distros nowadays only ship + PAE Kernels for x86 and there is no easy workaround. + floppy= [HW] See Documentation/blockdev/floppy.txt.
Hello kernel-team, regarding https://bugs.launchpad.net/ubuntu/+source/syslinux/+bug/930447 , i have developed a simple patch to (hopefully) provide an easy and elegant workaround/fix for the issue. I assume some hundred users (if not some thousand, as entries in bugreports are only the tip of an iceberg) are affected by this issue. Please take a review and feel free to merge. As defaulting to PAE kernels is specific for some distros only, i think this is no patch for mainline (yet). I did not often do patches, nor am i a good programmer - so sorry if the patch or the submission style is not perfect. regards Roland --- This patch adds a kernel bootparam "fixpae". If integrated into the kernel, this should make life more easy, as installation quirks like fake-pae package, upgrade path from ubuntu 12.04 onwards or specially crafted installation media are not needed anymore. Affected users also get a hint that their issue may be workarounded with this param. Just add the bootparam to the kernel commandline and you`re done. fixpae [x86] Workaround for a nasty PAE issue with older CPU`s like Pentium M, as they may report PAE incapability although they support it. This bootparam adds a fake pae entry to the flags section in /proc/cpuinfo and skips the validate_cpu() routine in arch/x86/boot/main.c This is necesssary as major distros nowadays only ship PAE Kernels for x86 and there is no easy workaround. signed-off-by: Roland Kletzing <devzero@web.de> ---