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

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

On 2021/12/20 4:29 PM, lijiang wrote:
> Hi, Qi
> Thank you for the fix.
>
> > Date: Thu, 16 Dec 2021 15:09:49 +0800
> > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > To: k-hagio-ab@xxxxxxx, ptesarik@xxxxxxxx, lijiang@xxxxxxxxxx
> > Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>, crash-utility@xxxxxxxxxx
> > Subject:  [PATCH] Fix pvops Xen detection for arm
> >          machine
> > Message-ID: <20211216070949.17668-1-zhengqi.arch@xxxxxxxxxxxxx>
> > Content-Type: text/plain; charset="US-ASCII"
> >
> > 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 above variable is statically defined in the kernel, but the
> 'xen_vcpu_info' is also a static variable, why does the former not
> work on arm machines, but the latter works well? Could you please
> explain more details?
> [linux]$ grep -nr "xen_vcpu_info" *
> arch/arm/xen/enlighten.c:51:static struct vcpu_info __percpu *xen_vcpu_info;

Hi Lianbo,

The 'xen_vcpu_info' is also a static variable on the arm/arm64 platform,
but different from 'xen_start_info', it is assigned during the
initialization process.

Thanks,
Qi

> Thanks.
> Lianbo
>
> > 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"
> >
> > For the arm/arm64 platform, fix it by using xen_vcpu_info instead of
> > xen_start_info to detect Xen dumps.
> >
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > ---
> >   kernel.c | 15 +++++++++++----
> >   1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel.c b/kernel.c
> > index f4598ea..4b4d789 100644
> > --- a/kernel.c
> > +++ b/kernel.c
> > @@ -10757,11 +10757,18 @@ 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)
> > +       if (machine_type("ARM") || machine_type("ARM64")) {
> > +               if (symbol_exists("xen_vcpu_info") &&
> > +                   readmem(symbol_value("xen_vcpu_info"), KVADDR, &addr,
> > +                   sizeof(void *), "xen_vcpu_info", RETURN_ON_ERROR) &&
> > +                   addr != 0)
> > +                       return TRUE;
> > +       } else 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;
> > +       }
> >
> >          return FALSE;
> >   }
> > --
> > 2.11.0

--
Thanks,
Qi

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