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Fri, 15 Aug 2025 08:18:30 -0400 X-MC-Unique: DnMuRJ1LP9yLqCBFUKR-Fg-1 X-Mimecast-MFC-AGG-ID: DnMuRJ1LP9yLqCBFUKR-Fg_1755260308 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5EA991800285; Fri, 15 Aug 2025 12:18:27 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.44.33.47]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 7CDB81800447; Fri, 15 Aug 2025 12:18:21 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 15 Aug 2025 14:17:10 +0200 (CEST) Date: Fri, 15 Aug 2025 14:17:03 +0200 From: Oleg Nesterov To: "Edgecombe, Rick P" Cc: "mingo@kernel.org" , "dave.hansen@linux.intel.com" , "bp@alien8.de" , "peterz@infradead.org" , "hpa@zytor.com" , "axboe@kernel.dk" , "tglx@linutronix.de" , "Mehta, Sohil" , "broonie@kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "debug@rivosinc.com" Subject: Re: [PATCH 5/6] x86/shstk: don't create the shadow stack for PF_USER_WORKERs Message-ID: <20250815121702.GB11549@redhat.com> References: <20250814101435.GA17362@redhat.com> <8818b456954644ce609e07d77a65714788ef9098.camel@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8818b456954644ce609e07d77a65714788ef9098.camel@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 On 08/14, Edgecombe, Rick P wrote: > > +Mark and Deepak > > On Thu, 2025-08-14 at 12:14 +0200, Oleg Nesterov wrote: > > If a features_enabled(ARCH_SHSTK_SHSTK) userspace thread creates a > > PF_USER_WORKER thread, shstk_alloc_thread_stack() allocates the shadow > > stack for no reason, the new (kernel) thread will never return to usermode. > > > > Plus the current code doesn't even look correct, in this case fpu_clone() > > won't call update_fpu_shstk(). ... > I agree we don't need to allocate a shadow stack in this case, Great, > but I'm not sure > it is right to fully disable shadow stack in thread.features. Why? > First of all, > disabling it from shstk_alloc_thread_stack() seems weird. It just handles > allocating shadow stacks. I agree in advance with any other change. > Lastly, it doesn't seem there is any way to clone from IO uring today, Not sure I understand... create_io_thread() ? > How about just adding the 'minimal' condition to: > if (clone_flags & CLONE_VFORK) { > shstk->base = 0; > shstk->size = 0; > return 0; > } > ...then update all the comments where vfork is called out as the only case that > does this? but create_io_thread() and vhost_task_create() do not use CLONE_VFORK? Oleg.