linux-kernel - [PATCH] KVM: x86/xen: Use a safer data type for delta to avoid shift-count-overflow

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Message-Id: <20220309064324.58213-1-likexu@tencent.com>
Date:   Wed,  9 Mar 2022 14:43:24 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Joao Martins <joao.m.martins@...cle.com>, kvm@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86/xen: Use a safer data type for delta to avoid shift-count-overflow

From: Like Xu <likexu@...cent.com>

Clang warns:

arch/x86/kvm/xen.c:1219:41: warning: right shift count >= width of type [-Wshift-count-overflow]
 1219 |         (delta > 0 && (uint32_t) (delta >> 50) != 0))) {
      |                                         ^~

The delta is long, which is 32-bit on ARCH=i386, hence the overflow
warning. Switch to uint64_t, which is 64-bit and will not overflow.

Fixes: 49c0b9159bce ("KVM: x86/xen: handle PV timers oneshot mode")
Signed-off-by: Like Xu <likexu@...cent.com>
---
 arch/x86/kvm/xen.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 8c85a71aa8ca..097181613be5 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1204,7 +1204,7 @@ static bool kvm_xen_hcall_set_timer_op(struct kvm_vcpu *vcpu, uint64_t timeout,
 
 	if (timeout) {
 		uint64_t guest_now = get_kvmclock_ns(vcpu->kvm);
-		long delta = timeout - guest_now;
+		uint64_t delta = timeout - guest_now;
 
 		/* Xen has a 'Linux workaround' in do_set_timer_op() which
 		 * checks for negative absolute timeout values (caused by
-- 
2.35.1