linux-kernel - [PATCH] KVM: x86/mmu: fix comparison of u8 with -1

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Message-Id: <20191126161255.323992-1-colin.king@canonical.com>
Date:   Tue, 26 Nov 2019 16:12:55 +0000
From:   Colin King <colin.king@...onical.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, clang-built-linux@...glegroups.com
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86/mmu: fix comparison of u8 with -1

From: Colin Ian King <colin.king@...onical.com>

The comparison of the u8 value __entry->u with -1 is always
going to be false because a __entry-u can never be negative.
Fix this by casting it to a s8 integer.

Addresses clang warning:
arch/x86/kvm/./mmutrace.h:360:16: warning: result of comparison
of constant -1 with expression of type 'u8' (aka 'unsigned char')
is always false [-Wtautological-constant-out-of-range-compare]

Fixes: 335e192a3fa4 ("KVM: x86: add tracepoints around __direct_map and FNAME(fetch)")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 arch/x86/kvm/mmutrace.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmutrace.h b/arch/x86/kvm/mmutrace.h
index 7ca8831c7d1a..3466cd528a67 100644
--- a/arch/x86/kvm/mmutrace.h
+++ b/arch/x86/kvm/mmutrace.h
@@ -357,7 +357,7 @@ TRACE_EVENT(
 		  __entry->r ? "r" : "-",
 		  __entry->spte & PT_WRITABLE_MASK ? "w" : "-",
 		  __entry->x ? "x" : "-",
-		  __entry->u == -1 ? "" : (__entry->u ? "u" : "-"),
+		  (s8)__entry->u == -1 ? "" : (__entry->u ? "u" : "-"),
 		  __entry->level, __entry->sptep
 	)
 );
-- 
2.24.0