linux-kernel - [PATCH] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu

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Message-ID: <20220509202355.13985-1-graf@amazon.com>
Date:   Mon, 9 May 2022 22:23:55 +0200
From:   Alexander Graf <graf@...zon.com>
To:     <kvm@...r.kernel.org>
CC:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Matt Evans <matt@...abs.org>, <stable@...r.kernel.org>
Subject: [PATCH] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context()

Commit 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
moved the switch_mmu_context() to C. While in principle a good idea, it
meant that the function now uses the stack. The stack is not accessible
from real mode though.

So to keep calling the function, let's turn on MSR_DR while we call it.
That way, all pointer references to the stack are handled virtually.

Reported-by: Matt Evans <matt@...abs.org>
Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
Signed-off-by: Alexander Graf <graf@...zon.com>
Cc: stable@...r.kernel.org
---
 arch/powerpc/kvm/book3s_32_sr.S | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S
index e3ab9df6cf19..bd4f798f7a46 100644
--- a/arch/powerpc/kvm/book3s_32_sr.S
+++ b/arch/powerpc/kvm/book3s_32_sr.S
@@ -122,11 +122,21 @@
 
 	/* 0x0 - 0xb */
 
-	/* 'current->mm' needs to be in r4 */
-	tophys(r4, r2)
-	lwz	r4, MM(r4)
-	tophys(r4, r4)
-	/* This only clobbers r0, r3, r4 and r5 */
+	/* switch_mmu_context() needs paging, let's enable it */
+	mfmsr   r9
+	ori     r11, r9, MSR_DR
+	mtmsr   r11
+	sync
+
+	/* Calling switch_mmu_context(<inv>, current->mm, <inv>); */
+	lwz	r4, MM(r2)
 	bl	switch_mmu_context
 
+	/* Disable paging again */
+	mfmsr   r9
+	li      r6, MSR_DR
+	andc    r9, r9, r6
+	mtmsr	r9
+	sync
+
 .endm
-- 
2.28.0.394.ge197136389




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