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From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Eirik Fuller <efuller@redhat.com>,
	kvm-ppc@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH v1 1/2] powerpc/64s: system call rfscv workaround for TM bugs
Date: Wed,  8 Sep 2021 20:17:17 +1000	[thread overview]
Message-ID: <20210908101718.118522-1-npiggin@gmail.com> (raw)

The rfscv instruction does not work correctly with the fake-suspend mode
in POWER9, which can end up with the hypervisor restoring an incorrect
checkpoint.

Work around this by setting the _TIF_RESTOREALL flag if a system call
returns to a transaction active state, causing rfid to be used instead
of rfscv to return, which will do the right thing. The contents of the
registers are irrelevant because they will be overwritten in this case
anyway.

Reported-by: Eirik Fuller <efuller@redhat.com>
Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/interrupt.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index c77c80214ad3..917a2ac4def6 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -139,6 +139,19 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	 */
 	irq_soft_mask_regs_set_state(regs, IRQS_ENABLED);
 
+	/*
+	 * If system call is called with TM active, set _TIF_RESTOREALL to
+	 * prevent RFSCV being used to return to userspace, because POWER9
+	 * TM implementation has problems with this instruction returning to
+	 * transactional state. Final register values are not relevant because
+	 * the transaction will be aborted upon return anyway. Or in the case
+	 * of unsupported_scv SIGILL fault, the return state does not much
+	 * matter because it's an edge case.
+	 */
+	if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) &&
+			unlikely(MSR_TM_TRANSACTIONAL(regs->msr)))
+		current_thread_info()->flags |= _TIF_RESTOREALL;
+
 	/*
 	 * If the system call was made with a transaction active, doom it and
 	 * return without performing the system call. Unless it was an
-- 
2.23.0


WARNING: multiple messages have this Message-ID (diff)
From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Eirik Fuller <efuller@redhat.com>,
	kvm-ppc@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH v1 1/2] powerpc/64s: system call rfscv workaround for TM bugs
Date: Wed, 08 Sep 2021 10:17:17 +0000	[thread overview]
Message-ID: <20210908101718.118522-1-npiggin@gmail.com> (raw)

The rfscv instruction does not work correctly with the fake-suspend mode
in POWER9, which can end up with the hypervisor restoring an incorrect
checkpoint.

Work around this by setting the _TIF_RESTOREALL flag if a system call
returns to a transaction active state, causing rfid to be used instead
of rfscv to return, which will do the right thing. The contents of the
registers are irrelevant because they will be overwritten in this case
anyway.

Reported-by: Eirik Fuller <efuller@redhat.com>
Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/interrupt.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index c77c80214ad3..917a2ac4def6 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -139,6 +139,19 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	 */
 	irq_soft_mask_regs_set_state(regs, IRQS_ENABLED);
 
+	/*
+	 * If system call is called with TM active, set _TIF_RESTOREALL to
+	 * prevent RFSCV being used to return to userspace, because POWER9
+	 * TM implementation has problems with this instruction returning to
+	 * transactional state. Final register values are not relevant because
+	 * the transaction will be aborted upon return anyway. Or in the case
+	 * of unsupported_scv SIGILL fault, the return state does not much
+	 * matter because it's an edge case.
+	 */
+	if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) &&
+			unlikely(MSR_TM_TRANSACTIONAL(regs->msr)))
+		current_thread_info()->flags |= _TIF_RESTOREALL;
+
 	/*
 	 * If the system call was made with a transaction active, doom it and
 	 * return without performing the system call. Unless it was an
-- 
2.23.0

             reply	other threads:[~2021-09-08 10:18 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 10:17 Nicholas Piggin [this message]
2021-09-08 10:17 ` [PATCH v1 1/2] powerpc/64s: system call rfscv workaround for TM bugs Nicholas Piggin
2021-09-08 10:17 ` [PATCH v1 2/2] KVM: PPC: Book3S HV: Tolerate treclaim. in fake-suspend mode changing registers Nicholas Piggin
2021-09-08 10:17   ` Nicholas Piggin
2021-09-17  8:02 ` [PATCH v1 1/2] powerpc/64s: system call rfscv workaround for TM bugs Daniel Axtens
2021-09-17  8:02   ` Daniel Axtens
2021-09-19 12:20 ` Michael Ellerman
2021-09-19 12:20   ` Michael Ellerman

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