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.