Re: [Crash-utility] [PATCH] arm64: Add fallback option when vabits_actual is missing

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.

+ 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; }