Re: [Crash-utility] [PATCH] Fix pvops Xen detection for arm machine

On 12/15/21 3:42 PM, HAGIO KAZUHITO(萩尾 一仁) wrote: > Hi Qi, Xen folks, > > -----Original Message----- >> Since the xen_start_info on the arm/arm64 platform is static defined: >> >> ./arm/xen/enlighten.c:40:static struct start_info _xen_start_info; >> ./arm/xen/enlighten.c:41:struct start_info *xen_start_info = >> &_xen_start_info; >> ./arm/xen/enlighten.c:42:EXPORT_SYMBOL(xen_start_info); >> >> The is_pvops_xen() in commit 4badc6229c69f5cd9da7eb7bdf400a53ec6db01a >> ("Fix pvops Xen detection for kernels >= v4.20") always return TRUE. >> Then the following error will be reported because p2m_mid_missing >> and xen_p2m_addr are not defined: >> >>     crash: cannot resolve "p2m_top" >> >> Fix it by using xen_vcpu_id instead of xen_start_info to detect Xen >> dumps. >> >> Signed-off-by: Qi Zheng <zhengqi.arch(a)bytedance.com&gt; >> --- >>   kernel.c | 21 ++++++++++++++++----- >>   1 file changed, 16 insertions(+), 5 deletions(-) >> >> diff --git a/kernel.c b/kernel.c >> index f4598ea..b216fbe 100644 >> --- a/kernel.c >> +++ b/kernel.c >> @@ -10745,6 +10745,9 @@ is_pvops_xen(void) >>   { >>       ulong addr; >>       char *sym; >> +    struct syment * sp; >> +    ulong ptr; >> +    int i; >> >>       if (!PVOPS()) >>           return FALSE; >> @@ -10757,11 +10760,19 @@ is_pvops_xen(void) >>            STREQ(sym, "paravirt_patch_default"))) >>           return TRUE; >> >> -    if (symbol_exists("xen_start_info") && >> -        readmem(symbol_value("xen_start_info"), KVADDR, &addr, >> -        sizeof(void *), "xen_start_info", RETURN_ON_ERROR) && >> -        addr != 0) >> -        return TRUE; >> +    sp = per_cpu_symbol_search("xen_vcpu_id"); >> +    if (sp) { >> +        for (i = 0; i < NR_CPUS; i++) { >> +            if (!kt->__per_cpu_offset[i]) >> +                continue; > > Thanks for the patch. > > But seems that kt->__per_cpu_offset is initialized after the > is_pvops_xen() > call.  So this block always return FALSE? > > Is there any other variable that we can use?  or another solution.. Or use xen_vcpu_info for arm/arm64 machine and xen_start_info for x86 machine? Both of these variables are assigned during the initialization path.

Thanks, Qi > > Thanks, > Kazu > >> + >> +            ptr = sp->value + kt->__per_cpu_offset[i]; >> +            if (ptr && readmem(ptr, KVADDR, &ptr, sizeof(uint32_t), >> +                "xen_vcpu_id", FAULT_ON_ERROR)) >> +                return TRUE; >> +            return FALSE; >> +        } >> +    } >> >>       return FALSE; >>   } >> -- >> 2.11.0