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Wed, 23 Sep 2026 00:49:29 -0700 (PDT) From: Magnus Lindholm To: richard.henderson@linaro.org, mattst88@gmail.com, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org Cc: linmag7@gmail.com, stable@vger.kernel.org Subject: [PATCH v3 2/7] alpha: only use a targeted tbi() when the target mm is really current Date: Wed, 23 Sep 2026 09:47:45 +0200 Message-ID: <20260923074903.862898-3-linmag7@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260923074903.862898-1-linmag7@gmail.com> References: <20260923074903.862898-1-linmag7@gmail.com> Precedence: bulk X-Mailing-List: linux-alpha@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ipi_flush_tlb_page() gates a targeted tbi() on current->active_mm. tbi() acts on the address space context currently loaded on the CPU, so it is only guaranteed to reach an mm's translations when a thread of that mm is running there. current->active_mm is not sufficient: under lazy TLB an idle or kernel task keeps an mm as its active_mm while a different ASN is loaded, so the invalidate is issued against the wrong context and the stale entry can survive. Nothing retires the old ASN afterwards either, mm->context[cpu] still being valid, so the resuming thread can reuse it. Test current->mm instead and otherwise fall back to flush_tlb_other(), which clears mm->context[cpu] and forces a fresh ASN at the next switch whatever is loaded now. This does not cover a task that borrowed an mm through kthread_use_mm(): both comparisons match such a task, which has current->mm set while ev5_switch_mm() has only prepared the PCB and nothing has issued the PAL_swpctx that installs it. asn_locked() does not identify that window either, for the reason given in the previous patch. Loading the context on a direct mm switch is what fixes that case, and is a separate change. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Magnus Lindholm --- arch/alpha/kernel/smp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c index ed06367ece57..1ad448105201 100644 --- a/arch/alpha/kernel/smp.c +++ b/arch/alpha/kernel/smp.c @@ -669,7 +669,8 @@ ipi_flush_tlb_page(void *x) struct flush_tlb_page_struct *data = x; struct mm_struct * mm = data->mm; - if (mm == current->active_mm && !asn_locked()) + /* A targeted tbi() needs a thread of MM to be current. */ + if (mm == current->mm && !asn_locked()) flush_tlb_current_page(mm, data->vma, data->addr); else flush_tlb_other(mm); -- 2.43.0