linux-kernel - Re: PF_USER_WORKERs and shadow stack

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Message-ID: <a4cb5e3e-717e-4a86-9e15-5b14ef322314@intel.com>
Date: Wed, 13 Aug 2025 09:41:48 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: PF_USER_WORKERs and shadow stack

On 8/13/25 09:28, Oleg Nesterov wrote:
> But it seems that if a features_enabled(ARCH_SHSTK_SHSTK) thread creates a
> PF_USER_WORKER thread, shstk_alloc_thread_stack() will allocate the shadow
> stack for no reason.

Is this costing us anything other than some CPU cycles and 160 bytes of
memory for a VMA?