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

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Mon, Nov 25, 2019 at 12:43:59PM -0500, Sasha Levin wrote:
> 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.

I don't think that will work, you'd also have to pull in commit 8daf346226b2
("KVM: x86: rename pte_list_remove to __pte_list_remove").  And e7912386ede8
in particular isn't stable material.

I'll send a proper backport for 4.19 and earlier, the conflicts should be
easy to resolve.