linux-kernel - Re: [PATCH v14 11/13] x86/mm: do targeted broadcast flushing from tlbbatch code

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: <20250304141134.GIZ8cKFom3W0ChHiXk@fat_crate.local>
Date: Tue, 4 Mar 2025 15:11:34 +0100
From: Borislav Petkov <bp@...en8.de>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Dave Hansen <dave.hansen@...el.com>, Rik van Riel <riel@...riel.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org,
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
	nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com,
	linux-mm@...ck.org, akpm@...ux-foundation.org, jannh@...gle.com,
	mhklinux@...look.com, andrew.cooper3@...rix.com,
	Manali.Shukla@....com, mingo@...nel.org
Subject: Re: [PATCH v14 11/13] x86/mm: do targeted broadcast flushing from
 tlbbatch code

On Tue, Mar 04, 2025 at 12:52:47PM +0000, Brendan Jackman wrote:
> https://lore.kernel.org/all/CA+i-1C31TrceZiizC_tng_cc-zcvKsfXLAZD_XDftXnp9B2Tdw@mail.gmail.com/

Lemme try to understand what you're suggesting on that subthread:

> static inline void arch_start_context_switch(struct task_struct *prev)
> {
>     arch_paravirt_start_context_switch(prev);
>     tlb_start_context_switch(prev);
> }

This kinda makes sense to me...

> Now I think about it... if we always tlbsync() before a context switch, is the
> cant_migrate() above actually required? I think with that, even if we migrated
> in the middle of e.g.  broadcast_kernel_range_flush(), we'd be fine? (At
> least, from the specific perspective of the invplgb code, presumably having
> preemption on there would break things horribly in other ways).

I think we still need it because you need to TLBSYNC on the same CPU you've
issued the INVLPGB and actually, you want all TLBs to have been synched
system-wide.

Or am I misunderstanding it?

Anything else I missed?

Btw, I just sent v15 - if you wanna continue commenting there...

https://lore.kernel.org/r/20250304135816.12356-1-bp@kernel.org

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette