Patch "KVM: Don't set Accessed/Dirty bits for ZERO_PAGE" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    KVM: Don't set Accessed/Dirty bits for ZERO_PAGE

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-don-t-set-accessed-dirty-bits-for-zero_page.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3264d8ebcbd8ce94ad77e4f218d175a952cc9d49
Author: Sean Christopherson <seanjc@xxxxxxxxxx>
Date:   Fri Apr 29 01:04:09 2022 +0000

    KVM: Don't set Accessed/Dirty bits for ZERO_PAGE
    
    [ Upstream commit a1040b0d42acf69bb4f6dbdc54c2dcd78eea1de5 ]
    
    Don't set Accessed/Dirty bits for a struct page with PG_reserved set,
    i.e. don't set A/D bits for the ZERO_PAGE.  The ZERO_PAGE (or pages
    depending on the architecture) should obviously never be written, and
    similarly there's no point in marking it accessed as the page will never
    be swapped out or reclaimed.  The comment in page-flags.h is quite clear
    that PG_reserved pages should be managed only by their owner, and
    strictly following that mandate also simplifies KVM's logic.
    
    Fixes: 7df003c85218 ("KVM: fix overflow of zero page refcount with ksm running")
    Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Message-Id: <20220429010416.2788472-4-seanjc@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c5dbac10c372..421b0ff72b46 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2339,16 +2339,28 @@ void kvm_release_pfn_dirty(kvm_pfn_t pfn)
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_dirty);
 
+static bool kvm_is_ad_tracked_pfn(kvm_pfn_t pfn)
+{
+	if (!pfn_valid(pfn))
+		return false;
+
+	/*
+	 * Per page-flags.h, pages tagged PG_reserved "should in general not be
+	 * touched (e.g. set dirty) except by its owner".
+	 */
+	return !PageReserved(pfn_to_page(pfn));
+}
+
 void kvm_set_pfn_dirty(kvm_pfn_t pfn)
 {
-	if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
+	if (kvm_is_ad_tracked_pfn(pfn))
 		SetPageDirty(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
 
 void kvm_set_pfn_accessed(kvm_pfn_t pfn)
 {
-	if (!kvm_is_reserved_pfn(pfn) && !kvm_is_zone_device_pfn(pfn))
+	if (kvm_is_ad_tracked_pfn(pfn))
 		mark_page_accessed(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);