linux-kernel - Re: [RFC] Restore PKRU to user-defined value after signal handling

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Message-ID: <19355174-c626-4f64-8158-820b393460d2@intel.com>
Date: Wed, 6 Nov 2024 11:47:16 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, "mingo@...hat.com"
 <mingo@...hat.com>, "dave.hansen@...ux.intel.com"
 <dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Rudi Horn <rudi.horn@...cle.com>, Joe Jin <joe.jin@...cle.com>,
 Jeff Xu <jeffxu@...omium.org>
Subject: Re: [RFC] Restore PKRU to user-defined value after signal handling

On 11/6/24 11:40, Aruna Ramakrishna wrote:
> I do not understand why it has to be moved. Would you mind explaining?

You need to know what XSTATE_BV value got written by XSAVE.  That's
dependent on: XINUSE and RFBM.

RFBM is 'mask' in xsave_to_user_sigframe().

So you can either completely regenerate 'mask' in
update_pkru_in_sigframe() or you can just pass 'mask' in.