linux-kernel - [PATCH] KVM: X86: fix lazy allocation of rmaps

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Message-Id: <20211015170507.136732-1-pbonzini@redhat.com>
Date:   Fri, 15 Oct 2021 13:05:07 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH] KVM: X86: fix lazy allocation of rmaps

If allocation of rmaps fails, but some of the pointers have already been written,
those pointers can be cleaned up when the memslot is freed, or even reused later
for another attempt at allocating the rmaps.  Therefore there is no need to
WARN, as done for example in memslot_rmap_alloc, but the allocation *must* be
skipped lest KVM will overwrite the previous pointer and will indeed leak memory.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 07f5760ea30c..cba7a99374bc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11392,7 +11392,8 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
 		int level = i + 1;
 		int lpages = __kvm_mmu_slot_lpages(slot, npages, level);

-		WARN_ON(slot->arch.rmap[i]);
+		if (slot->arch.rmap[i])
+			continue;

 		slot->arch.rmap[i] = vcalloc(lpages, sz);
 		if (!slot->arch.rmap[i]) {
-- 
2.27.0