Re: FAILED: patch "[PATCH] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved" failed to apply to 4.19-stable tree

[Sasha Levin <sashal@kernel.org>]

On Mon, Nov 18, 2019 at 04:22:40PM +0100, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.19-stable tree.
>If someone wants it applied there, or to any other stable or longterm
>tree, then please email the backport, including the original git commit
>id to <stable@vger.kernel.org>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From a78986aae9b2988f8493f9f65a587ee433e83bc3 Mon Sep 17 00:00:00 2001
>From: Sean Christopherson <sean.j.christopherson@intel.com>
>Date: Mon, 11 Nov 2019 14:12:27 -0800
>Subject: [PATCH] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
>
>Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and
>instead manually handle ZONE_DEVICE on a case-by-case basis.  For things
>like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal
>pages, e.g. put pages grabbed via gup().  But for flows such as setting
>A/D bits or shifting refcounts for transparent huge pages, KVM needs to
>to avoid processing ZONE_DEVICE pages as the flows in question lack the
>underlying machinery for proper handling of ZONE_DEVICE pages.
>
>This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup()
>when running a KVM guest backed with /dev/dax memory, as KVM straight up
>doesn't put any references to ZONE_DEVICE pages acquired by gup().
>
>Note, Dan Williams proposed an alternative solution of doing put_page()
>on ZONE_DEVICE pages immediately after gup() in order to simplify the
>auditing needed to ensure is_zone_device_page() is called if and only if
>the backing device is pinned (via gup()).  But that approach would break
>kvm_vcpu_{un}map() as KVM requires the page to be pinned from map() 'til
>unmap() when accessing guest memory, unlike KVM's secondary MMU, which
>coordinates with mmu_notifier invalidations to avoid creating stale
>page references, i.e. doesn't rely on pages being pinned.
>
>[*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl
>
>Reported-by: Adam Borowski <kilobyte@angband.pl>
>Analyzed-by: David Hildenbrand <david@redhat.com>
>Acked-by: Dan Williams <dan.j.williams@intel.com>
>Cc: stable@vger.kernel.org
>Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
>Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

I also took e7912386ede8 ("KVM: x86: reintroduce pte_list_remove, but
including mmu_spte_clear_track_bits") and queued both for 4.19-4.9.

-- 
Thanks,
Sasha