linux-kernel - [PATCH 4.4 026/312] MIPS: KVM: Fix translation of MFC0 ErrCtl

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Message-Id: <20200508123126.325941201@linuxfoundation.org>
Date:   Fri,  8 May 2020 14:30:17 +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, James Hogan <james.hogan@...tec.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
        kvm@...r.kernel.org
Subject: [PATCH 4.4 026/312] MIPS: KVM: Fix translation of MFC0 ErrCtl

From: James Hogan <james.hogan@...tec.com>

commit 66ffc50c480e7ab6ad5642f47276435a8873c31a upstream.

The MIPS KVM dynamic translation is meant to translate "MFC0 rt, ErrCtl"
instructions into "ADD rt, zero, zero" to zero the destination register,
however the rt register number was copied into rt of the ADD instruction
encoding, which is the 2nd source operand. This results in "ADD zero,
zero, rt" which is a no-op, so only the first execution of each such
MFC0 from ErrCtl will actually read 0.

Fix the shift to put the rt from the MFC0 encoding into the rd field of
the ADD.

Fixes: 50c8308538dc ("KVM/MIPS32: Binary patching of select privileged instructions.")
Signed-off-by: James Hogan <james.hogan@...tec.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: linux-mips@...ux-mips.org
Cc: kvm@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/kvm/dyntrans.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/mips/kvm/dyntrans.c
+++ b/arch/mips/kvm/dyntrans.c
@@ -82,7 +82,7 @@ int kvm_mips_trans_mfc0(uint32_t inst, u
 
 	if ((rd == MIPS_CP0_ERRCTL) && (sel == 0)) {
 		mfc0_inst = CLEAR_TEMPLATE;
-		mfc0_inst |= ((rt & 0x1f) << 16);
+		mfc0_inst |= ((rt & 0x1f) << 11);
 	} else {
 		mfc0_inst = LW_TEMPLATE;
 		mfc0_inst |= ((rt & 0x1f) << 16);