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Thu, 20 Aug 2026 14:47:56 +0000 (GMT) Received: from [9.124.211.198] (unknown [9.124.211.198]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 20 Aug 2026 14:47:56 +0000 (GMT) Message-ID: <2e16b624-be55-4127-8ec8-db9479957f96@linux.ibm.com> Date: Thu, 20 Aug 2026 20:17:55 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] powerpc/entry: Fix irq_soft_mask corruption on replayed interrupt exit To: "Mukesh Kumar Chaurasiya (IBM)" Cc: Venkat Rao Bagalkote , maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, mchauras@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <20260820134718.2176411-1-mkchauras@gmail.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260820134718.2176411-1-mkchauras@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=CpuPtH4D c=1 sm=1 tr=0 ts=6a8713a4 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=pGLkceISAAAA:8 a=EF15BPeV1vtgjPpHrm0A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: zBcC0yL-Jw3oirLsSa2NFJa-9rJ-pP95 X-Proofpoint-GUID: HUkEiR7KcZau7RJEXTP2WQucqc7rk5Pr X-Proofpoint-Spam-Info: AW1haW4tMjYwODIwMDEwOSBTYWx0ZWRfXx9MX6ouHHvyv BHXnFNUxOuPgmNKR9/SA89Cjy4+O8f7F3agoHy/GMcsDlmB/aJD/BXEXvDTNOSCaEROtBwRQ0rm MxoO0r//Uajqj5UJpcp+EVmdMozIT1M= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODIwMDEwOSBTYWx0ZWRfX+dTLzNyocqGR 31InRShjt7eK8Ct2v6XPpw8+nh5gng3HNZFKhe75U81Uu1fCUnrU4pa0yE1Y4UgvZFRZhOru7Ch MOQP0LWSDbHruhRiLMRTnkMfjW4tYWZbzgzuhiV1Pcg5TLLWVYAOrlz3aHe+SpvSYQGMzHczidd iJBKqba6ti8l829dEJOFokvN5MMKCP77rAU4QOUNnM/TuCvDIQWF+LKt/iMdb4fq0ypLcfUVvB9 jjyORQmfmt5imjVTYFdP1RHtKu0YyPDUsMOuNofqk+WYNyoRJ1lxcFpWGhMzkvISVY0a/aRu6Vv 8s9evny/dsrs9Ps3+5Zj4/jPQVsIrpJNh0/Agne95EcazGKuFSnjL/2MLZgjPnHI2lHH0ZXP2hX Ph0zUtgt9uipISnDGD0EDGzl+zA9bVTu45WE4VwwAyVkw9SLLzdyySvBLji+Q5F8plBrCKExAd0 PMusEy44/Pzf2027FNQ== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-19_06,2026-08-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 bulkscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 spamscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608200109 On 8/20/26 7:17 PM, Mukesh Kumar Chaurasiya (IBM) wrote: > When __replay_soft_interrupts() replays a pending interrupt (e.g. > PACA_IRQ_DEC → timer_interrupt), it calls the handler directly with a > synthetic pt_regs. The DEFINE_INTERRUPT_HANDLER_ASYNC wrapper around > each handler calls arch_interrupt_async_exit_prepare() on the way out, > which calls arch_interrupt_exit_prepare() → local_irq_disable() → > arch_local_irq_disable(), which does: > > irq_soft_mask_set(IRQS_DISABLED) /* 0x1 */ > > This unconditionally overwrites irq_soft_mask with IRQS_DISABLED (0x1), > stripping the IRQS_PMI_DISABLED (0x2) bit. The result is that > irq_soft_mask is 0x1 instead of IRQS_ALL_DISABLED (0x3) when the > handler returns to __replay_soft_interrupts(). > > For a normally-taken interrupt this is harmless: the next interrupt > always enters through arch_interrupt_enter_prepare() which > unconditionally sets irq_soft_mask to IRQS_ALL_DISABLED. > But during replay, next_interrupt() is called > directly between replayed handlers without going back through > arch_interrupt_enter_prepare(), so the stripped bit is never restored. > next_interrupt() then fires a WARNING: > > WARNING: arch/powerpc/kernel/irq_64.c:75 > WARN_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED) > > This was introduced by commit bee25f97ad24 ("powerpc: Enable > GENERIC_ENTRY feature"). Before that commit, the old > interrupt_async_exit_prepare() called irq_exit() followed by an empty > interrupt_exit_prepare() stub and never touched irq_soft_mask at all, > so the soft mask was left at IRQS_ALL_DISABLED throughout replay. > > The root cause: arch_interrupt_exit_prepare() uses local_irq_disable() > whose only job is to set the IRQS_DISABLED bit; it has no knowledge of > IRQS_PMI_DISABLED. It is there to satisfy irqentry_exit()'s > requirement that interrupts be disabled, but using the plain > irq_soft_mask_set(IRQS_ALL_DISABLED) is the right primitive: > > - irq_soft_mask_set(IRQS_ALL_DISABLED): sets soft mask to 0x3 > (both IRQS_DISABLED and IRQS_PMI_DISABLED). Touches only the soft > mask. MSR[EE] and PACA_IRQ_HARD_DIS are already correct because > hard interrupts were never re-enabled during replay > (PACA_IRQ_REPLAYING is in PACA_IRQ_MUST_HARD_MASK, which blocks > should_hard_irq_enable()). > > - local_irq_disable() / arch_local_irq_disable(): sets soft mask to > IRQS_DISABLED (0x1) only, silently dropping IRQS_PMI_DISABLED. > > - hard_irq_disable(): also issues __mtmsrd to clear MSR[EE] in > hardware and sets PACA_IRQ_HARD_DIS — redundant and wrong here > since both are already set. > > Fix by replacing local_irq_disable() with irq_soft_mask_set(IRQS_ALL_DISABLED) > in arch_interrupt_exit_prepare(), making the exit symmetric with the > entry path in arch_interrupt_enter_prepare() which always sets > IRQS_ALL_DISABLED. > > The warning was observed early in boot on a POWER10 pseries guest > during kmem_cache_init_late(), where a spinlock release triggers > interrupt replay that processes a pending timer interrupt. > > Debugger state confirming the bug: > Before timer_interrupt(®s): > irq_soft_mask = 0x3 (IRQS_ALL_DISABLED) correct > irq_happened = 0x41 (HARD_DIS|REPLAYING) correct > After timer_interrupt(®s) returns: > irq_soft_mask = 0x1 (IRQS_DISABLED) WRONG — PMI bit stripped > irq_happened = 0x41 unchanged > Indeed. Thanks for the fix and good explanation. Reviewed-by: Shrikanth Hegde > Fixes: 334f3f6d7a16 ("powerpc/entry: Disable interrupts before irqentry_exit") > Reported-by: Venkat Rao Bagalkote > Closes: https://lore.kernel.org/all/6f9bfb0f-b14c-468e-bb9f-c157d120d0dc@linux.ibm.com/ > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) > --- > Change log: > V1 -> V2: > - Instead of using hard_irq_disable use irq_soft_mask_set > V1: https://lore.kernel.org/all/20260812152035.1661781-1-mkchauras@gmail.com > > arch/powerpc/include/asm/entry-common.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h > index c5adb5006361..2a153dca962c 100644 > --- a/arch/powerpc/include/asm/entry-common.h > +++ b/arch/powerpc/include/asm/entry-common.h > @@ -270,7 +270,7 @@ static inline void arch_interrupt_exit_prepare(struct pt_regs *regs) > } > > /* irqentry_exit expects to be called with interrupts disabled */ > - local_irq_disable(); > + irq_soft_mask_set(IRQS_ALL_DISABLED); > } > > static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs)