[Crash-utility] [PATCH v3] arm64/x86_64: show zero pfn information when using vtop

[lijiang]

Hi, Rongwei
Thank you for the patch.
On Tue, May 16, 2023 at 8:00 PM <crash-utility-request at redhat.com> wrote:

> Date: Tue, 16 May 2023 19:40:54 +0800
> From: Rongwei Wang <rongwei.wang at linux.alibaba.com>
> To: crash-utility at redhat.com,   k-hagio-ab at nec.com
> Subject: [Crash-utility] [PATCH v3] arm64/x86_64: show zero pfn
>         information when using vtop
> Message-ID: <20230516114054.63844-1-rongwei.wang at linux.alibaba.com>
> Content-Type: text/plain; charset="US-ASCII"; x-default=true
>
> Now vtop can not show us the page is zero pfn
> when PTE or PMD has attached ZERO PAGE. This
> patch supports show this information directly
> when using vtop, likes:
>
> crash> vtop -c 13674 ffff8917e000
> VIRTUAL     PHYSICAL
> ffff8917e000  836e71000
>
> PAGE DIRECTORY: ffff000802f8d000
>    PGD: ffff000802f8dff8 => 884e29003
>    PUD: ffff000844e29ff0 => 884e93003
>    PMD: ffff000844e93240 => 840413003
>    PTE: ffff000800413bf0 => 160000836e71fc3
>   PAGE: 836e71000  (ZERO PAGE)
> ...
>
> If huge page found:
>
> crash> vtop -c 14538 ffff95800000
> VIRTUAL     PHYSICAL
> ffff95800000  910c00000
>
> PAGE DIRECTORY: ffff000801fa0000
>    PGD: ffff000801fa0ff8 => 884f53003
>    PUD: ffff000844f53ff0 => 8426cb003
>    PMD: ffff0008026cb560 => 60000910c00fc1
>   PAGE: 910c00000  (2MB, ZERO PAGE)
> ...
>
>
I did some tests on x86 64 and aarch64 machines, and got the following
results.

[1] on x86 64, it does not print the "ZERO PAGE" when using 1G huge pages.
(but for 2M huge page, it works)
crash> vtop -c 2763 7fdfc0000000
VIRTUAL     PHYSICAL
7fdfc0000000  300000000

   PGD: 23b9ae7f8 => 8000000235031067
   PUD: 235031bf8 => 80000003000008e7
  PAGE: 300000000  (1GB)

      PTE         PHYSICAL   FLAGS
80000003000008e7  300000000  (PRESENT|RW|USER|ACCESSED|DIRTY|PSE|NX)

      VMA           START       END     FLAGS FILE
ffff9d65fc8a85c0 7fdfc0000000 7fe000000000 84400fb /mnt/hugetlbfs/test

      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffef30cc000000 300000000 ffff9d65f5c35850        0  2 57ffffc001000c
uptodate,dirty,head

crash> help -v|grep zero
         zero_paddr: 221a37000
    huge_zero_paddr: 240000000

[2] on aarch64, it does not print the "ZERO PAGE"
crash> vtop -c 23390 ffff8d600000
VIRTUAL     PHYSICAL
ffff8d600000  cc800000

PAGE DIRECTORY: ffff224ba02d9000
   PGD: ffff224ba02d9ff8 => 80000017b38f003
   PUD: ffff224b7b38fff0 => 80000017b38e003
   PMD: ffff224b7b38e358 => e80000cc800f41
  PAGE: cc800000  (2MB)

     PTE        PHYSICAL  FLAGS
e80000cc800f41  cc800000  (VALID|USER|SHARED|AF|NG|PXN|UXN|DIRTY)

      VMA           START       END     FLAGS FILE
ffff224bb315f678 ffff8d600000 ffff8d800000 4400fb /mnt/hugetlbfs/test

      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
fffffc892b320000  cc800000 ffff224b5c48ac90        0  2 7ffff80001000c
uptodate,dirty,head
crash> help -v|grep zero
         zero_paddr: 142662000
    huge_zero_paddr: 111400000

I have one question:  can this patch print "ZERO PAGE" on x86 64 when using
1G huge pages? Or is it expected behavior on x86 64?

And It does not work on aarch64 machine to me. Did I miss anything else?

Thanks
Lianbo
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