[Crash-utility] [PATCH] arm64 : assign page_offset and kvbase based on VA_BITS passed

[lijiang]

On Thu, Oct 14, 2021 at 11:17 AM HAGIO KAZUHITO(萩尾　一仁)
<k-hagio-ab at nec.com> wrote:
>
> Hi Ankur,
>
> -----Original Message-----
> >       >> assign page_offset and kvbase based on VA_BITS passed
> >       >>
> >
> >       >Thank you for the patch, Ankur.
> >       >Can you help to describe the reason in detail? And what happened?
> >
> >
> >
> > Hi Lianbo, Raw ramdump without vmcoreinfo doesn't work here.
> > read_vmcoreinfo("NUMBER(BA_BITS)") will not work on raw ramdump.
> > getting below error
> >

Thank you for the information, Ankur.

> > crash_64: vmlinux and /var/tmp/ramdump_elf_XUtCMT do not match!
> > Usage:
> > crash [OPTION]... NAMELIST MEMORY-IMAGE[@address <https://github.com/address> ] (dumpfile form)
> > crash [OPTION]... [NAMELIST] (live system form)
> > Enter "crash_64 -h" for details.
> >
> > Recent change https://github.com/crash-utility/crash/commit/167d37e347fe35c6f7db826e8539e192c4375564 is
> > causing this issue, before this change VA_BITS_ACTUAL was used which is passed from cmd line.
>
> ok, I see, but I'm not sure why your patch uses the (pc->flags2 & SNAP) condition.

This seems not  very reasonable, the SNAP flag has a specific use.

> The calculation used VA_BITS_ACTUAL (== VA_BITS for ramdump) before the change,
> so how about the following patch?
>./crash
> diff --git a/arm64.c b/arm64.c
> index 7069312671cf..da78acbb013f 100644
> --- a/arm64.c
> +++ b/arm64.c
> @@ -4031,6 +4031,9 @@ arm64_calc_VA_BITS(void)
>                                 error(FATAL, "cannot determine VA_BITS_ACTUAL\n");
>                 }
>
> +               if (!machdep->machspec->CONFIG_ARM64_VA_BITS) /* guess */
> +                       machdep->machspec->CONFIG_ARM64_VA_BITS = machedp->machspec->VA_BITS;
> +

Looks good.

>                 /*
>                  * The mm flip commit is introduced before 52-bits VA, which is before the
>                  * commit to export NUMBER(TCR_EL1_T1SZ)
>

BTW: Can we also try to get its value from kernel config? But this
relies on kernel config: CONFIG_IKCONFIG.

diff --git a/arm64.c b/arm64.c
index 7069312..79f9929 100644
--- a/arm64.c
+++ b/arm64.c
@@ -3989,6 +3989,10 @@ arm64_calc_VA_BITS(void)
                value = atol(string);
                free(string);
                machdep->machspec->CONFIG_ARM64_VA_BITS = value;
+       } else if (kt->ikconfig_flags & IKCONFIG_AVAIL) {
+               if ((get_kernel_config("CONFIG_ARM64_VA_BITS",
+                       &string)) == IKCONFIG_STR)
+                       machdep->machspec->CONFIG_ARM64_VA_BITS = atol(string);
        }

        if (kernel_symbol_exists("vabits_actual")) {

Thanks.
Lianbo
> > 3987 static void
> > 3988 arm64_calc_VA_BITS(void)
> > 3989 {
> > 3990     int bitval;
> > 3991     struct syment *sp;
> > 3992     ulong vabits_actual, value;
> > 3993     char *string;
> > 3994
> > 3995     if ((string = pc->read_vmcoreinfo("NUMBER(VA_BITS)"))) {
> > 3996         value = atol(string);
> > 3997         free(string);
> > 3998         machdep->machspec->CONFIG_ARM64_VA_BITS = value;
> > 3999     }
> >
> >
> >
> >
> >       >Thanks.
> >       >Lianbo
> >
> >       >> Change-Id: I525f3c7fd91e1f06e909c2f4c1749c44c068baea
> >       >> Signed-off-by: Ankur Bansal <er.ankurbansal at gmail.com <mailto:er.ankurbansal at gmail.com> >
> >       >> ---
> >       >> arm64.c | 15 +++++++++++----
> >       >> 1 file changed, 11 insertions(+), 4 deletions(-)
> >       >>
> >       >> diff --git a/arm64.c b/arm64.c
> >       >> index 7069312..2dc77f7 100644
> >       >> --- a/arm64.c
> >       >> +++ b/arm64.c
> >       >> @@ -220,10 +220,17 @@ arm64_init(int when)
> >       >>
> >       >>                 /* vabits_actual introduced after mm flip, so it should be flipped layout */
> >       >>                 if (ms->VA_BITS_ACTUAL) {
> >       >> -                       ms->page_offset = ARM64_FLIP_PAGE_OFFSET;
> >       >> -                       /* useless on arm64 */
> >       >> -                       machdep->identity_map_base = ARM64_FLIP_PAGE_OFFSET;
> >       >> -                       machdep->kvbase = ARM64_FLIP_PAGE_OFFSET;
> >       >> +                       if ((pc->flags2 & SNAP)) {
> >       >> +                               ms->page_offset = ARM64_FLIP_PAGE_OFFSET;
> >       >> +                               /* useless on arm64 */
> >       >> +                               machdep->identity_map_base = ARM64_FLIP_PAGE_OFFSET;
> >       >> +                               machdep->kvbase = ARM64_FLIP_PAGE_OFFSET;
> >       >> +                       }
> >       >> +                       else{
> >       >> +                               ms->page_offset = ARM64_FLIP_PAGE_OFFSET_ACTUAL;
> >       >> +                               machdep->identity_map_base = ARM64_FLIP_PAGE_OFFSET_ACTUAL;
> >       >> +                               machdep->kvbase = ARM64_FLIP_PAGE_OFFSET_ACTUAL;
> >       >> +                       }
> >       >>                         ms->userspace_top = ARM64_USERSPACE_TOP_ACTUAL;
> >       >>                 } else {
> >       >>                         ms->page_offset = ARM64_PAGE_OFFSET;
> >       >> --
> >       >> 2.7.4
> >
> >
> >
> >       ------------------------------
> >
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> >
> >       End of Crash-utility Digest, Vol 192, Issue 28
> >       **********************************************
> >
> >
> >
>