Messages in this thread | | | Subject | Re: [PATCH] s390/setup: fix early warning messages | From | Guenter Roeck <> | Date | Mon, 18 Feb 2019 11:22:40 -0800 |
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Hi Cornelia,
On 2/18/19 10:16 AM, Cornelia Huck wrote: > On Mon, 18 Feb 2019 18:21:06 +0100 > Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: > >> On Mon, 18 Feb 2019 18:01:46 +0100 >> Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: >> >>> On Mon, 18 Feb 2019 07:46:40 -0800 >>> Guenter Roeck <linux@roeck-us.net> wrote: >>> >>>> Hi, >>>> >>>> On Thu, Feb 14, 2019 at 03:40:56PM +0100, Martin Schwidefsky wrote: >>>>> The setup_lowcore() function creates a new prefix page for the boot CPU. >>>>> The PSW mask for the system_call, external interrupt, i/o interrupt and >>>>> the program check handler have the DAT bit set in this new prefix page. >>>>> >>>>> At the time setup_lowcore is called the system still runs without virtual >>>>> address translation, the paging_init() function creates the kernel page >>>>> table and loads the CR13 with the kernel ASCE. >>>>> >>>>> Any code between setup_lowcore() and the end of paging_init() that has >>>>> a BUG or WARN statement will create a program check that can not be >>>>> handled correctly as there is no kernel page table yet. >>>>> >>>>> To allow early WARN statements initially setup the lowcore with DAT off >>>>> and set the DAT bit only after paging_init() has completed. >>>>> >>>>> Cc: stable@vger.kernel.org >>>>> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> >>>> >>>> This patch causes s390 qemu emulations to crash with a kernel stack overflow. >>>> Reverting the patch fixes the problem. Crash log and bisect results below. >>> >>> Urgs, yes. That is EDAT-1 again that makes it work with 1MB pages but breaks >>> with 4K mapping where the prefix page is mapped to absolute zero. >>> >>> Just using S390_lowcore instead of lowcore_ptr[0] does not work either >>> because low-address protection is already active. I'll think of something. >>> >>> Thanks for bug report! >> >> This patch should fix the problem: >> -- >> From d4393e82c3ec9b2fe5dba4b0d1b6eef29f8d15c8 Mon Sep 17 00:00:00 2001 >> From: Martin Schwidefsky <schwidefsky@de.ibm.com> >> Date: Mon, 18 Feb 2019 18:10:08 +0100 >> Subject: [PATCH] s390/setup: fix boot crash for machine without EDAT-1 >> >> The fix to make WARN work in the early boot code created a problem >> on older machines without EDAT-1. The setup_lowcore_dat_on function >> uses the pointer from lowcore_ptr[0] to set the DAT bit in the new >> PSWs. That does not work if the kernel page table is set up with >> 4K pages as the prefix address maps to absolute zero. >> >> To make this work the PSWs need to be changed with via address 0 in >> form of the S390_lowcore definition. >> >> Cc: stable@vger.kernel.org >> Fixes: 94f85ed3e2 ("s390/setup: fix early warning messages") >> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> >> --- >> arch/s390/kernel/setup.c | 13 ++++++------- >> 1 file changed, 6 insertions(+), 7 deletions(-) >> >> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c >> index 65b22ef5141a..12934e8fbb91 100644 >> --- a/arch/s390/kernel/setup.c >> +++ b/arch/s390/kernel/setup.c >> @@ -451,13 +451,12 @@ static void __init setup_lowcore_dat_off(void) >> >> static void __init setup_lowcore_dat_on(void) >> { >> - struct lowcore *lc; >> - >> - lc = lowcore_ptr[0]; >> - lc->external_new_psw.mask |= PSW_MASK_DAT; >> - lc->svc_new_psw.mask |= PSW_MASK_DAT; >> - lc->program_new_psw.mask |= PSW_MASK_DAT; >> - lc->io_new_psw.mask |= PSW_MASK_DAT; >> + __ctl_clear_bit(0, 28); >> + S390_lowcore.external_new_psw.mask |= PSW_MASK_DAT; >> + S390_lowcore.svc_new_psw.mask |= PSW_MASK_DAT; >> + S390_lowcore.program_new_psw.mask |= PSW_MASK_DAT; >> + S390_lowcore.io_new_psw.mask |= PSW_MASK_DAT; >> + __ctl_set_bit(0, 28); >> } >> >> static struct resource code_resource = { > > I could reproduce the crash under qemu/tcg and with this patch on top > it is gone. >
What is your qemu command line ?
Thanks, Guenter
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