stable inclusion
from stable-5.10.19
commit d2cbae37c3d8f9ce1f33ae690421be6ecf3809d1
bugzilla: 50607

--------------------------------

commit 8fc51726 upstream.

Walk the list of MMU pages in reverse in kvm_mmu_zap_oldest_mmu_pages().
The list is FIFO, meaning new pages are inserted at the head and thus
the oldest pages are at the tail.  Using a "forward" iterator causes KVM
to zap MMU pages that were just added, which obliterates guest
performance once the max number of shadow MMU pages is reached.

Fixes: 6b82ef2c ("KVM: x86/mmu: Batch zap MMU pages when recycling oldest pages")
Reported-by: NZdenek Kaspar <zkaspar82@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210113205030.3481307-1-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>