linux-kernel - Re: [PATCH v3 0/3] SRF: Fix offline CPU preventing pc6 entry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1ee47890-7f19-4c21-9d0d-94834d716159@linux.intel.com>
Date: Tue, 12 Nov 2024 16:43:21 +0100
From: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 rafael.j.wysocki@...el.com, len.brown@...el.com,
 artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH v3 0/3] SRF: Fix offline CPU preventing pc6 entry

> There's a comment there that explains why this is done. If you don't
> understand this, then please don't touch this code.

/*
 * Kexec is about to happen. Don't go back into mwait() as
 * the kexec kernel might overwrite text and data including
 * page tables and stack. So mwait() would resume when the
 * monitor cache line is written to and then the CPU goes
 * south due to overwritten text, page tables and stack.
 *
 * Note: This does _NOT_ protect against a stray MCE, NMI,
 * SMI. They will resume execution at the instruction
 * following the HLT instruction and run into the problem
 * which this is trying to prevent.
 */

If you are referring to this comment above, I do understand the need to
enter hlt loop before the kexec happens. I thought that I could bring
all of the offlined CPUs back online, effectively getting them out of
the mwait loop.