linux-kernel - Re: [RFC PATCH v2 2/3] x86/mm/tlb: Defer PTI flushes

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]

Date:   Tue, 27 Aug 2019 11:28:53 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC PATCH v2 2/3] x86/mm/tlb: Defer PTI flushes

On 8/23/19 3:52 PM, Nadav Amit wrote:
> INVPCID is considerably slower than INVLPG of a single PTE. Using it to
> flush the user page-tables when PTI is enabled therefore introduces
> significant overhead.

I'm not sure this is worth all the churn, especially in the entry code.
 For large flushes (> tlb_single_page_flush_ceiling), we don't do
INVPCIDs in the first place.

I'd really want to understand what the heck is going on that makes
INVPCID so slow, first.