[Crash-utility] ramdump support for va_bits_actual

[vinayak menon]

Hi Dave,

On Sat, Apr 18, 2020 at 2:08 PM Dave Anderson <anderson at redhat.com> wrote:
>
>
>
> ----- Original Message -----
> > Hi Dave,
> >
> > Noticed that raw ramdumps of 5.4 kernel aren't working with crash tip.
> > With the patches attached, I could get it working. Please take a look.
> >
> > Thanks,
> > Vinayak
> >
>
> Hi Vinayak,
>
> A couple quick questions come to mind...
>
> First, I haven't checked all possible READMEM plugins, but for example, if this
> function is run on a live system, the -1 file descriptor would cause the READMEM()
> call to fail:


I changed it like this and it works for ramdump. I don't actually have
a live setup to try this. Let me try
to set up one.

diff --git a/arm64.c b/arm64.c
index 04efc13..fce3f8e 100644
--- a/arm64.c
+++ b/arm64.c
@@ -981,7 +981,7 @@ arm64_calc_physvirt_offset(void)

        if ((sp = kernel_symbol_search("physvirt_offset")) &&
                        machdep->machspec->kimage_voffset) {
-               if (READMEM(-1, &physvirt_offset, sizeof(physvirt_offset),
+               if (READMEM(pc->mfd, &physvirt_offset, sizeof(physvirt_offset),
                        sp->value, sp->value -
                        machdep->machspec->kimage_voffset) > 0) {
                                ms->physvirt_offset = physvirt_offset;


>
>  static void
> +arm64_calc_physvirt_offset(void)
> +{
> +       struct machine_specific *ms = machdep->machspec;
> +       ulong physvirt_offset;
> +       struct syment *sp;
> +
> +       ms->physvirt_offset = ms->phys_offset - ms->page_offset;
> +
> +       if ((sp = kernel_symbol_search("physvirt_offset")) &&
> +                       machdep->machspec->kimage_voffset) {
> +               if (READMEM(-1, &physvirt_offset, sizeof(physvirt_offset),
> +                       sp->value, sp->value -
> +                       machdep->machspec->kimage_voffset) > 0) {
> +                               ms->physvirt_offset = physvirt_offset;
> +               }
> +       }
> +
> +       if (CRASHDEBUG(1))
> +               fprintf(fp, "using %lx as physvirt_offset\n", ms->physvirt_offset);
> +}
>
> And here -- are you missing some brackets?  (run "make warn")
>

I did try "make warn" and it does not show any issues.Am I missing something ?


> But regardless of that, why are you setting it back to 48 if it's greater than 48?
>


I did that because machspec->CONFIG_ARM64_VA_BITS is used for calculation of
vmemmap size. In kernel vmemmap size is calculated using VA_BITS_MIN and it is
defined like this

#if VA_BITS > 48
#define VA_BITS_MIN             (48)
#else
#define VA_BITS_MIN             (VA_BITS)
#endif

But I realize now that its not the right thing to do, because
machspec->CONFIG_ARM64_VA_BITS
is later used in arm64_calc_VA_BITS to verify machspec->VA_BITS. So
what about this ?

diff --git a/arm64.c b/arm64.c
index 04efc13..a35a30e 100644
--- a/arm64.c
+++ b/arm64.c
@@ -4023,8 +4023,6 @@ arm64_calc_virtual_memory_ranges(void)
                        if ((ret = get_kernel_config("CONFIG_ARM64_VA_BITS",
                                        &string)) == IKCONFIG_STR)

machdep->machspec->CONFIG_ARM64_VA_BITS = atol(string);
-                               if
(machdep->machspec->CONFIG_ARM64_VA_BITS > 48)
-
machdep->machspec->CONFIG_ARM64_VA_BITS = 48;
                }
        }

@@ -4049,7 +4047,12 @@ arm64_calc_virtual_memory_ranges(void)
 #define STRUCT_PAGE_MAX_SHIFT   6

        if (ms->VA_BITS_ACTUAL) {
-               vmemmap_size = (1UL) << (ms->CONFIG_ARM64_VA_BITS -
machdep->pageshift - 1 + STRUCT_PAGE_MAX_SHIFT);
+               ulong va_bits_min = 48;
+
+               if (machdep->machspec->CONFIG_ARM64_VA_BITS < 48)
+                       va_bits_min = ms->CONFIG_ARM64_VA_BITS;
+
+               vmemmap_size = (1UL) << (va_bits_min -
machdep->pageshift - 1 + STRUCT_PAGE_MAX_SHIFT);
                vmalloc_end = (- PUD_SIZE - vmemmap_size - KILOBYTES(64));
                vmemmap_start = (-vmemmap_size);
                ms->vmalloc_end = vmalloc_end - 1;

Thanks,
Vinayak

>
> Thanks,
>   Dave
>
> --
> Crash-utility mailing list
> Crash-utility at redhat.com
> https://www.redhat.com/mailman/listinfo/crash-utility
>