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Tue, 03 Nov 2026 01:47:03 -0800 (PST) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36a428af4e6sm38668145eec.4.2026.11.03.01.46.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 01:47:02 -0800 (PST) From: Ritesh Harjani (IBM) To: "Christophe Leroy (CS GROUP)" , linuxppc-dev@lists.ozlabs.org Cc: Madhavan Srinivasan , Venkat Rao Bagalkote , linux-kernel@vger.kernel.org, Michael Ellerman , Nicholas Piggin , Hari Bathini , stable@vger.kernel.org, Josef Schlehofer Subject: Re: [PATCH] powerpc/code-patching: Flush the patch area TLB entry locally In-Reply-To: <44406eef-0035-4d6f-a2b0-3647d7c1ea2e@kernel.org> Date: Tue, 03 Nov 2026 14:42:04 +0530 Message-ID: References: <44406eef-0035-4d6f-a2b0-3647d7c1ea2e@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit "Christophe Leroy (CS GROUP)" writes: > Le 03/11/2026 à 03:54, Ritesh Harjani (IBM) a écrit : >> patching functions like patch_mem() and patch_instructions(), maps the >> target page at the per-cpu text_poke_area, write it, clear the PTE and >> then flushes the tlb using flush_tlb_kernel_range(), with interrupts >> disabled. flush_tlb_kernel_range() on SMP nohash (e500) does an IPI >> based TLB invalidation i.e - >> >> smp_call_function(do_flush_tlb_mm_ipi, NULL, 1); >> >> ...which will wait for other CPUs but with interrupts off. This can be >> caught by lockdep with the following warning: >> >> WARNING: kernel/smp.c:917 at smp_call_function_many_cond+0x430/0x818, CPU#1: swapper/0/1 >> CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.3.0-rc1-leds-v4 #1 PREEMPT >> Hardware name: Turris 1.1 e500v2 0x80211051 Freescale P2020 >> Call Trace: >> [c1915bc0] [c001be04] flush_tlb_kernel_range+0x2c/0x74 >> [c1915bd0] [c001ce2c] patch_instructions+0x1b0/0x318 >> [c1915c20] [c003113c] bpf_arch_text_copy+0x5c/0xb4 >> [c1915c40] [c01c3398] bpf_jit_binary_pack_finalize+0x28/0x8c >> [c1915c60] [c0031770] bpf_int_jit_compile+0x5dc/0x758 >> ... >> [c1915dd0] [c102e114] ptp_classifier_init+0x30/0x4c >> [c1915df0] [c102d3a8] sock_init+0xc8/0xe4 >> ... >> hardirqs last disabled at (3076): [] patch_instructions+0x238/0x318 >> >> Josef confirmed that this was causing a hang (deadlock): >> I think this is why the CZ.NIC Turris 1.1 hangs early in boot with >> CONFIG_JUMP_LABEL=y. On 6.18.44 it hung in 19 of 19 boots and booted >> fine 9 of 9 times with jump labels off. The hang comes while static >> keys are patched and modules are loaded, nothing is printed and the >> watchdog resets the board. OpenWrt keeps jump labels off on these >> boards for now. >> >> ...which is possible if both cpus are doing similar operations with interrupts >> off and doing TLB invalidation using IPI. >> >> Broadcast TLB invalidation is not needed here since text_poke_area is >> a per-cpu area. It is mapped and unmapped with interrupts disabled by >> it's own cpu. The only reason I think, if we would need a broadcast tlb >> invalidate is, when we want to prevent a stray or malicious write to >> this cpu text_poke_area by another CPU. This generally gets solved with >> temporary-mm path like how Radix and even x86 implements. However, booke >> doesn't implement that, so for now let's ensure we use local tlb >> flushing for correctness. > > This problem was already discussed one year ago, see > https://lore.kernel.org/all/PA3P192MB2865C07D634E3B775D003C7F8CD7A@PA3P192MB2865.EURP192.PROD.OUTLOOK.COM/ > > See response from Arnd, a stop_machine() should be done for completeness. > I will have to take sometime to go over what ARM does here with stop_machine(). However, either ways I think, we still need this fix, since otherwise P2020 boards gets hung during boot. Thoughts? >> >> Fixes: 49e3d8ea6248 ("powerpc/fsl_booke: Enable STRICT_KERNEL_RWX") >> Cc: stable@vger.kernel.org >> Reported-by: Josef Schlehofer >> Closes: https://lore.kernel.org/all/20261026195644.16384-1-pepe.schlehofer@gmail.com/ >> Tested-by: Josef Schlehofer >> Signed-off-by: Ritesh Harjani (IBM) >> --- >> arch/powerpc/lib/code-patching.c | 21 +++++++++++++++++++-- >> 1 file changed, 19 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c >> index 44ff9f684bef..6351342fa5c3 100644 >> --- a/arch/powerpc/lib/code-patching.c >> +++ b/arch/powerpc/lib/code-patching.c >> @@ -276,6 +276,23 @@ static int __do_patch_mem_mm(void *addr, unsigned long val, bool is_dword) >> return err; >> } >> >> +/* >> + * The patch area is per-CPU and only used by its own CPU, with IRQs >> + * disabled, so only the local TLB can hold an entry for it. >> + * >> + * On nohash SMP, flush_tlb_kernel_range() IPIs the other CPUs and waits, which >> + * must not be done with IRQs disabled (see smp_call_function_many_cond()), so >> + * flush just the local kernel (PID 0) entry. >> + * Book3S keeps flush_tlb_kernel_range() which doesn't IPI here. >> + */ >> +static void flush_patch_area(unsigned long addr) >> +{ >> + if (IS_ENABLED(CONFIG_PPC_BOOK3S)) > > CONFIG_PPC_BOOK3S not consistant with commit message. Are you adressing > a problem on e500 only ? on all not book3s ? What about book3s/32 ? What > about 8xx ? Even for book3s/64, is it correct at all when > mm_patch_enabled() returns false ? > No we are addressing the problem on all NOHASH platforms. IIUC, all !BOOK3S are "nohash". Although some of them maybe UP, so it doesn't matter whether a flush_tlb_kernel_range() is called or local_flush_tlb_page() - it wouldn't matter. And on others which are SMP but do not have STRICT_KERNEL_RWX enabled, they will anyway not go through this path - but if they ever do - then we should ensure they too do a local_flush_tlb_range() to avoid the same deadlock. However, I think, maybe we could use CONFIG_PPC_MMU_NOHASH instead of using CONFIG_PPC_BOOK3S, thoughts? -ritesh >> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); >> + else >> + local_flush_tlb_page(NULL, addr); >> +} >> + >> static int __do_patch_mem(void *addr, unsigned long val, bool is_dword) >> { >> int err; >> @@ -296,7 +313,7 @@ static int __do_patch_mem(void *addr, unsigned long val, bool is_dword) >> err = __patch_mem(addr, val, patch_addr, is_dword); >> >> pte_clear(&init_mm, text_poke_addr, pte); >> - flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE); >> + flush_patch_area(text_poke_addr); >> >> return err; >> } >> @@ -488,7 +505,7 @@ static int __do_patch_instructions(u32 *addr, u32 *code, size_t len, bool repeat >> err = __patch_instructions(patch_addr, code, len, repeat_instr); >> >> pte_clear(&init_mm, text_poke_addr, pte); >> - flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE); >> + flush_patch_area(text_poke_addr); >> >> return err; >> } >> -- >> 2.39.5 >>