linux-kernel - [PATCH 5.8 156/177] KVM: arm64: Do not try to map PUDs when they are folded into PMD

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Message-Id: <20200915140701.167300561@linuxfoundation.org>
Date:   Tue, 15 Sep 2020 16:13:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Gavin Shan <gshan@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Marc Zyngier <maz@...nel.org>
Subject: [PATCH 5.8 156/177] KVM: arm64: Do not try to map PUDs when they are folded into PMD

From: Marc Zyngier <maz@...nel.org>

commit 3fb884ffe921c99483a84b0175f3c03f048e9069 upstream.

For the obscure cases where PMD and PUD are the same size
(64kB pages with 42bit VA, for example, which results in only
two levels of page tables), we can't map anything as a PUD,
because there is... erm... no PUD to speak of. Everything is
either a PMD or a PTE.

So let's only try and map a PUD when its size is different from
that of a PMD.

Cc: stable@...r.kernel.org
Fixes: b8e0ba7c8bea ("KVM: arm64: Add support for creating PUD hugepages at stage 2")
Reported-by: Gavin Shan <gshan@...hat.com>
Reported-by: Eric Auger <eric.auger@...hat.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@....com>
Reviewed-by: Gavin Shan <gshan@...hat.com>
Tested-by: Gavin Shan <gshan@...hat.com>
Tested-by: Eric Auger <eric.auger@...hat.com>
Tested-by: Alexandru Elisei <alexandru.elisei@....com>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/kvm/mmu.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1968,7 +1968,12 @@ static int user_mem_abort(struct kvm_vcp
 		(fault_status == FSC_PERM &&
 		 stage2_is_exec(kvm, fault_ipa, vma_pagesize));
 
-	if (vma_pagesize == PUD_SIZE) {
+	/*
+	 * If PUD_SIZE == PMD_SIZE, there is no real PUD level, and
+	 * all we have is a 2-level page table. Trying to map a PUD in
+	 * this case would be fatally wrong.
+	 */
+	if (PUD_SIZE != PMD_SIZE && vma_pagesize == PUD_SIZE) {
 		pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
 
 		new_pud = kvm_pud_mkhuge(new_pud);