On Thu, Dec 08, 2022 at 02:23:55AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> On 2022/12/07 13:25, Pavan Kondeti wrote:
> > On Wed, Dec 07, 2022 at 02:01:56AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> >> Thanks for the patch.
> >>
> >> On 2022/12/06 19:00, Pavankumar Kondeti wrote:
> >>> After the commit 0d9b1ffefabe ("arm64: mm: make vabits_actual
> >>> a build time constant if possible") introduced in v5.19
> >>> Linux kernel, the crash will not find vabits_actual symbol.
> >>
> >> "if VA_BITS <= 48" ?
> >>
> > Thats right.
> >
> >>> Add a fallback option to initialize VA_BITS based on the
> >>> user supplied machdep options.
> >>>
> >>> Tested ramdumps loading in both 6.0 and 5.15 kernels.
> >>
> >> What if kernels < 5.4? For such old kernels without vabits_actual
> >> introduced, probably we should not set VA_BITS_ACTUAL..
> >>
> >>
> > ok, so what if the user passes -m vabits_actual=X on an older kernel dumps.
>
> I think it's ok to fail, because they should not use that option
> for older kernels than 5.4, it's a wrong usage.
>
Makes sense. I only started passing -m vabits_actual=N for 5.10+ kernel dumps.
>
> + if (machdep->machspec->CONFIG_ARM64_VA_BITS) {
> + /* guess */
> + machdep->machspec->VA_BITS_ACTUAL = machdep->machspec->CONFIG_ARM64_VA_BITS;
>
> This is my concern. Actually I found a 4.18.0 arm64 vmcore with
> NUMBER(VA_BITS)=48 in vmcoreinfo, crash fails to start with the patch.
>
> # crash-arm64 vmlinux vmcore
> ...
> crash-arm64: read error: kernel virtual address: fffff6003bcc0050 type: "IRQ stack pointer"
> crash-arm64: read error: kernel virtual address: fffff6003bcf0050 type: "IRQ stack pointer"
> crash-arm64: read error: kernel virtual address: fffff6003fffe400 type: "memory section root table"
> #
>
> > Earlier we ignore it, but now we end up using it. should I add a kernel
> > version check in fallback() routine?
>
> hmm, currently THIS_KERNEL_VERSION cannot be used at the point.
> We need to fill it, but also need vmcoreinfo..
>
>
> um, please let me know if I misunderstand, I don't have arm64
> knowledge very much.
>
> Do ramdumps need "-m vabits_actual=xx" regardless of the
> existence of vabits_actual symbol on 5.4 and later?
>
> And it seems that recent arm64 vmcores have NUMBER(TCR_EL1_T1SZ)
> in vmcoreinfo, they are covered by arm64_set_va_bits_by_tcr().
>
> so how about adding only this?
>
> --- a/arm64.c
> +++ b/arm64.c
> @@ -4671,6 +4671,10 @@ arm64_calc_VA_BITS(void)
> return;
> } else if (arm64_set_va_bits_by_tcr()) {
> return;
> + } else if (machdep->machspec->VA_BITS_ACTUAL) {
> + machdep->machspec->VA_BITS = machdep->machspec->VA_BITS_ACTUAL;
> + machdep->machspec->VA_START = _VA_START(machdep->machspec->VA_BITS_ACTUAL);
> + return;
> }
>
This works and looks simple. I have resent the patch.
PS: I am not on the list. so please keep me in to/cc while replying.
Thanks,
Pavan
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