From: Alexander Graf <graf@amazon.com>
To: <kvm@vger.kernel.org>
Cc: <linuxppc-dev@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Paul Mackerras <paulus@samba.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Matt Evans <matt@ozlabs.org>, <stable@vger.kernel.org>
Subject: [PATCH v3] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context()
Date: Tue, 10 May 2022 14:37:17 +0200 [thread overview]
Message-ID: <20220510123717.24508-1-graf@amazon.com> (raw)
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.
In addition, make sure to save/restore r12 on the stack, as it may get
clobbered by the C function.
Reported-by: Matt Evans <matt@ozlabs.org>
Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
Signed-off-by: Alexander Graf <graf@amazon.com>
Cc: stable@vger.kernel.org # v5.14+
---
v1 -> v2:
- Save and restore R12, so that we don't touch volatile registers
while calling into C.
v2 -> v3:
- Save and restore R12 on the stack. SPRGs may be clobbered by
page faults.
---
arch/powerpc/kvm/book3s_32_sr.S | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S
index e3ab9df6cf19..6cfcd20d4668 100644
--- a/arch/powerpc/kvm/book3s_32_sr.S
+++ b/arch/powerpc/kvm/book3s_32_sr.S
@@ -122,11 +122,27 @@
/* 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
+
+ /* switch_mmu_context() clobbers r12, rescue it */
+ SAVE_GPR(12, r1)
+
+ /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */
+ lwz r4, MM(r2)
bl switch_mmu_context
+ /* restore r12 */
+ REST_GPR(12, r1)
+
+ /* Disable paging again */
+ mfmsr r9
+ li r6, MSR_DR
+ andc r9, r9, r6
+ mtmsr r9
+ sync
+
.endm
--
2.28.0.394.ge197136389
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
WARNING: multiple messages have this Message-ID (diff)
From: Alexander Graf <graf@amazon.com>
To: <kvm@vger.kernel.org>
Cc: Matt Evans <matt@ozlabs.org>,
linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
stable@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH v3] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context()
Date: Tue, 10 May 2022 14:37:17 +0200 [thread overview]
Message-ID: <20220510123717.24508-1-graf@amazon.com> (raw)
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.
In addition, make sure to save/restore r12 on the stack, as it may get
clobbered by the C function.
Reported-by: Matt Evans <matt@ozlabs.org>
Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C")
Signed-off-by: Alexander Graf <graf@amazon.com>
Cc: stable@vger.kernel.org # v5.14+
---
v1 -> v2:
- Save and restore R12, so that we don't touch volatile registers
while calling into C.
v2 -> v3:
- Save and restore R12 on the stack. SPRGs may be clobbered by
page faults.
---
arch/powerpc/kvm/book3s_32_sr.S | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S
index e3ab9df6cf19..6cfcd20d4668 100644
--- a/arch/powerpc/kvm/book3s_32_sr.S
+++ b/arch/powerpc/kvm/book3s_32_sr.S
@@ -122,11 +122,27 @@
/* 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
+
+ /* switch_mmu_context() clobbers r12, rescue it */
+ SAVE_GPR(12, r1)
+
+ /* Calling switch_mmu_context(<inv>, current->mm, <inv>); */
+ lwz r4, MM(r2)
bl switch_mmu_context
+ /* restore r12 */
+ REST_GPR(12, r1)
+
+ /* Disable paging again */
+ mfmsr r9
+ li r6, MSR_DR
+ andc r9, r9, r6
+ mtmsr r9
+ sync
+
.endm
--
2.28.0.394.ge197136389
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
next reply other threads:[~2022-05-10 12:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 12:37 Alexander Graf [this message]
2022-05-10 12:37 ` [PATCH v3] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context() Alexander Graf
2022-05-13 7:53 ` Christophe Leroy
2022-05-13 7:53 ` Christophe Leroy
2022-05-15 10:34 ` Michael Ellerman
2022-05-15 10:34 ` Michael Ellerman
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