From: Oleg Nesterov <oleg@redhat.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Jens Axboe <axboe@kernel.dk>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: PF_USER_WORKERs and shadow stack
Date: Wed, 13 Aug 2025 21:14:42 +0200 [thread overview]
Message-ID: <20250813191441.GA26754@redhat.com> (raw)
In-Reply-To: <a4cb5e3e-717e-4a86-9e15-5b14ef322314@intel.com>
On 08/13, Dave Hansen wrote:
>
> 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?
Well, I guess no, but I do have another reason for "something-like-this" cleanup.
I am working on other changes which should eliminate x86_task_fpu(PF_USER_WORKER).
Hopefully I'll send the patches tomorrow. To remind, see
https://lore.kernel.org/all/20250812125700.GA11290@redhat.com/
So I'd like to ensure that ssp_active() can't return T in ssp_get().
And... Dave, I understand that it is very easy to criticize someone else's code ;)
But - if I am right - the current logic doesn't look clean to me. Regardless.
Oleg.
next prev parent reply other threads:[~2025-08-13 19:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-13 16:28 PF_USER_WORKERs and shadow stack Oleg Nesterov
2025-08-13 16:41 ` Dave Hansen
2025-08-13 19:14 ` Oleg Nesterov [this message]
2025-08-13 19:20 ` Oleg Nesterov
2025-08-13 19:21 ` Dave Hansen
2025-08-14 10:12 ` Oleg Nesterov
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