linux-kernel - [PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

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Message-Id: <20200305002422.20968-1-sean.j.christopherson@intel.com>
Date:   Wed,  4 Mar 2020 16:24:22 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86: Fix warning due to implicit truncation on 32-bit KVM

Explicitly cast the integer literal to an unsigned long when stuffing a
non-canonical value into the host virtual address during private memslot
deletion.  The explicit cast fixes a warning that gets promoted to an
error when running with KVM's newfangled -Werror setting.

  arch/x86/kvm/x86.c:9739:9: error: large integer implicitly truncated
  to unsigned type [-Werror=overflow]

Fixes: a3e967c0b87d3 ("KVM: Terminate memslot walks via used_slots"
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/x86.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ba4d476b79ad..fa03f31ab33c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9735,8 +9735,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		if (!slot || !slot->npages)
 			return 0;
 
-		/* Stuff a non-canonical value to catch use-after-delete. */
-		hva = 0xdeadull << 48;
+		/*
+		 * Stuff a non-canonical value to catch use-after-delete.  This
+		 * ends up being 0 on 32-bit KVM, but there's no better
+		 * alternative.
+		 */
+		hva = (unsigned long)(0xdeadull << 48);
 		old_npages = slot->npages;
 	}
 
-- 
2.24.1