Re: [PATCH] vfio/type1: unpin PageReserved page

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


在 2024/2/27 18:27, David Hildenbrand 写道:
On 26.02.24 18:32, Alex Williamson wrote:
On Tue, 27 Feb 2024 01:14:54 +0800
Yisheng Xie <ethan.xys@xxxxxxxxxxxxxxxxx> wrote:

在 2024/2/27 00:14, Alex Williamson 写道:
On Tue, 27 Feb 2024 00:01:06 +0800
Yisheng Xie<ethan.xys@xxxxxxxxxxxxxxxxx>  wrote:
We meet a warning as following:
   WARNING: CPU: 99 PID: 1766859 at mm/gup.c:209 try_grab_page.part.0+0xe8/0x1b0    CPU: 99 PID: 1766859 Comm: qemu-kvm Kdump: loaded Tainted: GOE  5.10.134-008.2.x86_64 #1

Does this issue reproduce on mainline?  Thanks,

I have check the code of mainline, the logical seems the same as my

so I think it can reproduce if i understand correctly.

I obviously can't speak to what's in your 5.10.134-008.2 kernel, but I
do know there's a very similar issue resolved in v6.0 mainline and
included in v5.10.146 of the stable tree.  Please test.  Thanks,

This commit, to be precise:

commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4
Author: Alex Williamson <alex.williamson@xxxxxxxxxx>
Date:   Mon Aug 29 21:05:40 2022 -0600

    vfio/type1: Unpin zero pages
        There's currently a reference count leak on the zero page.  We increment     the reference via pin_user_pages_remote(), but the page is later handled
    as an invalid/reserved page, therefore it's not accounted against the
    user and not unpinned by our put_pfn().
        Introducing special zero page handling in put_pfn() would resolve the
    leak, but without accounting of the zero page, a single user could
    still create enough mappings to generate a reference count overflow.
        The zero page is always resident, so for our purposes there's no reason
    to keep it pinned.  Therefore, add a loop to walk pages returned from
    pin_user_pages_remote() and unpin any zero pages.


in the meantime, we also have

commit c8070b78751955e59b42457b974bea4a4fe00187
Author: David Howells <dhowells@xxxxxxxxxx>
Date:   Fri May 26 22:41:40 2023 +0100

    mm: Don't pin ZERO_PAGE in pin_user_pages()
        Make pin_user_pages*() leave a ZERO_PAGE unpinned if it extracts a pointer     to it from the page tables and make unpin_user_page*() correspondingly     ignore a ZERO_PAGE when unpinning.  We don't want to risk overrunning a
    zero page's refcount as we're only allowed ~2 million pins on it -
    something that userspace can conceivably trigger.
        Add a pair of functions to test whether a page or a folio is a ZERO_PAGE.

So the unpin_user_page_* won't do anything with the shared zeropage.

(likely, we could revert 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4)

Thanks for your detail info. BTW, do we need handle all of the pagereserved page?

[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]

  Powered by Linux