FAILED: patch "[PATCH] KVM: Play nice with read-only memslots when querying host" failed to apply to 5.5-stable tree

FAILED: patch "[PATCH] KVM: Play nice with read-only memslots when querying host" failed to apply to 5.5-stable tree

[gregkh]

The patch below does not apply to the 5.5-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 42cde48b2d39772dba47e680781a32a6c4b7dc33 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Wed, 8 Jan 2020 12:24:38 -0800
Subject: [PATCH] KVM: Play nice with read-only memslots when querying host
 page size

Avoid the "writable" check in __gfn_to_hva_many(), which will always fail
on read-only memslots due to gfn_to_hva() assuming writes.  Functionally,
this allows x86 to create large mappings for read-only memslots that
are backed by HugeTLB mappings.

Note, the changelog for commit 05da45583de9 ("KVM: MMU: large page
support") states "If the largepage contains write-protected pages, a
large pte is not used.", but "write-protected" refers to pages that are
temporarily read-only, e.g. read-only memslots didn't even exist at the
time.

Fixes: 4d8b81abc47b ("KVM: introduce readonly memslot")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
[Redone using kvm_vcpu_gfn_to_memslot_prot. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f6f8ffc2e865..eb3709d55139 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1409,7 +1409,7 @@ unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn)
 
 	size = PAGE_SIZE;
 
-	addr = kvm_vcpu_gfn_to_hva(vcpu, gfn);
+	addr = kvm_vcpu_gfn_to_hva_prot(vcpu, gfn, NULL);
 	if (kvm_is_error_hva(addr))
 		return PAGE_SIZE;
 

Re: FAILED: patch "[PATCH] KVM: Play nice with read-only memslots when querying host" failed to apply to 5.5-stable tree

[Sasha Levin]

On Sun, Feb 09, 2020 at 01:36:52PM +0100, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 5.5-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 42cde48b2d39772dba47e680781a32a6c4b7dc33 Mon Sep 17 00:00:00 2001
>From: Sean Christopherson <sean.j.christopherson@intel.com>
>Date: Wed, 8 Jan 2020 12:24:38 -0800
>Subject: [PATCH] KVM: Play nice with read-only memslots when querying host
> page size
>
>Avoid the "writable" check in __gfn_to_hva_many(), which will always fail
>on read-only memslots due to gfn_to_hva() assuming writes.  Functionally,
>this allows x86 to create large mappings for read-only memslots that
>are backed by HugeTLB mappings.
>
>Note, the changelog for commit 05da45583de9 ("KVM: MMU: large page
>support") states "If the largepage contains write-protected pages, a
>large pte is not used.", but "write-protected" refers to pages that are
>temporarily read-only, e.g. read-only memslots didn't even exist at the
>time.
>
>Fixes: 4d8b81abc47b ("KVM: introduce readonly memslot")
>Cc: stable@vger.kernel.org
>Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>[Redone using kvm_vcpu_gfn_to_memslot_prot. - Paolo]
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

I'm not sure what was wrong with 5.5-4.14, it applied/built fine for me.

For 4.9 and 4.4, it depends on f9b84e19221e ("KVM: Use vcpu-specific
gva->hva translation when querying host page size") which wasn't
backported that far, so this one should also be backported to 4.9 and
4.4.

-- 
Thanks,
Sasha