[Crash-utility] [PATCH] arm64: Use VA_BITS for page_offset calculation

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Pingfan, Lianbo,

-----Original Message-----
> On Mon, Oct 25, 2021 at 4:43 PM HAGIO KAZUHITO(萩尾　一仁)
> <k-hagio-ab at nec.com> wrote:
> >
> > Hi,
> >
> > Here is a patch for the issue reported by Ankur.
> > Could you help test this with your ramdumps and arm64 machines?
> >
> The patch looks good to me. And I will schedule a machine to have a test.

Pingfan, thank you for the check and test, it's very helpful.

Ankur told me that the patch was working fine.

Lianbo, my understanding is that to get a raw ramdump, hardware functionality
or something is required.  But maybe you can reproduce a similar situation
with QEMU memory dump without vmcoreinfo?  e.g. on RHEL:

  # virsh dump <domain> domain.dump --memory-only

but you may need a kernel configured with VA_BITS=48 to reproduce and check
the fix, I guess.

Thanks,
Kazu

> 
> Regards,
> Pingfan
> > --
> > From 028ddf655c847c16cce23198017d2ff0169bb4de Mon Sep 17 00:00:00 2001
> > From: Kazuhito Hagio <k-hagio-ab at nec.com>
> > Date: Mon, 25 Oct 2021 16:53:26 +0900
> > Subject: [PATCH] arm64: Use VA_BITS for page_offset calculation
> >
> > Commit 167d37e347fe ("arm64: assign page_offset with VA_BITS kernel
> > configuration value") changed the page_offset calculation from
> > using VA_BITS_ACTUAL to CONFIG_ARM64_VA_BITS.  This caused an error
> > for ramdumps without vmcoreinfo like this:
> >
> >   crash: vmlinux and /var/tmp/ramdump_elf_XUtCMT do not match!
> >
> > Set the vmcoreinfo value to VA_BITS if available, and use VA_BITS
> > for page_offset calculation instead.
> >
> > Also remove ARM64_FLIP_PAGE_OFFSET_ACTUAL because it's not used
> > actually.
> >
> > Reported-by: Ankur Bansal <er.ankurbansal at gmail.com>
> > Signed-off-by: Kazuhito Hagio <k-hagio-ab at nec.com>
> > ---
> >  arm64.c | 5 ++++-
> >  defs.h  | 4 +---
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/arm64.c b/arm64.c
> > index 7069312671cf..3dcbcc642fda 100644
> > --- a/arm64.c
> > +++ b/arm64.c
> > @@ -404,7 +404,7 @@ arm64_init(int when)
> >                                 fprintf(fp, "CONFIG_ARM64_VA_BITS: %ld\n", ms->CONFIG_ARM64_VA_BITS);
> >                                 fprintf(fp, "      VA_BITS_ACTUAL: %ld\n", ms->VA_BITS_ACTUAL);
> >                                 fprintf(fp, "(calculated) VA_BITS: %ld\n", ms->VA_BITS);
> > -                               fprintf(fp, " PAGE_OFFSET: %lx\n", ARM64_FLIP_PAGE_OFFSET_ACTUAL);
> > +                               fprintf(fp, " PAGE_OFFSET: %lx\n", ARM64_FLIP_PAGE_OFFSET);
> >                                 fprintf(fp, "    VA_START: %lx\n", ms->VA_START);
> >                                 fprintf(fp, "     modules: %lx - %lx\n", ms->modules_vaddr,
> ms->modules_end);
> >                                 fprintf(fp, "     vmalloc: %lx - %lx\n", ms->vmalloc_start_addr,
> ms->vmalloc_end);
> > @@ -4031,6 +4031,9 @@ arm64_calc_VA_BITS(void)
> >                                 error(FATAL, "cannot determine VA_BITS_ACTUAL\n");
> >                 }
> >
> > +               if (machdep->machspec->CONFIG_ARM64_VA_BITS)
> > +                       machdep->machspec->VA_BITS = machdep->machspec->CONFIG_ARM64_VA_BITS;
> > +
> >                 /*
> >                  * The mm flip commit is introduced before 52-bits VA, which is before the
> >                  * commit to export NUMBER(TCR_EL1_T1SZ)
> > diff --git a/defs.h b/defs.h
> > index 8b356d5e8959..971005596506 100644
> > --- a/defs.h
> > +++ b/defs.h
> > @@ -3238,9 +3238,7 @@ typedef signed int s32;
> >  #define ARM64_PAGE_OFFSET    ((0xffffffffffffffffUL) \
> >                                         << (machdep->machspec->VA_BITS - 1))
> >  /* kernels >= v5.4 the kernel VA space is flipped */
> > -#define ARM64_FLIP_PAGE_OFFSET (-(1UL) << machdep->machspec->CONFIG_ARM64_VA_BITS)
> > -#define ARM64_FLIP_PAGE_OFFSET_ACTUAL ((0xffffffffffffffffUL) \
> > -                                       - ((1UL) << machdep->machspec->VA_BITS_ACTUAL) + 1)
> > +#define ARM64_FLIP_PAGE_OFFSET (-(1UL) << machdep->machspec->VA_BITS)
> >
> >  #define ARM64_USERSPACE_TOP  ((1UL) << machdep->machspec->VA_BITS)
> >  #define ARM64_USERSPACE_TOP_ACTUAL  ((1UL) << machdep->machspec->VA_BITS_ACTUAL)
> > --
> > 2.27.0
> >