linux-kernel - Re: [PATCH 15/24] x86/mm: Allow flushing for future ASID switches

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: <d5abe842-66dc-7365-0f54-7de6b61d06df@linux.intel.com>
Date:   Thu, 30 Nov 2017 10:53:11 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 15/24] x86/mm: Allow flushing for future ASID switches

On 11/30/2017 10:48 AM, Andy Lutomirski wrote:
>> __flush_tlb() does a flushing CR3 write that flushes the current PCID.
>> If we need other PCIDs flushed, we have to do it via the
>> tlb_flush_shared_nonglobals() mechanism.
>>
>> Does it matter today in practice?  Nope, we never have that situation.
>> But, it also doesn't _hurt_ to have that line there in any way.
> Should it be tlb_flush_shared_nonglobals_if_kernel_and_user_pagetables_are_separate()?

The separate page tables doesn't play into it as far as I can tell.  the
important thing is that you have "stuff" in some other *kernel* address
space that you didn't flush.

> The whole idea that we can get away with ambiguous functions like
> __flush_tlb() seems to be much less true with KAISER.  I think we
> should maybe start getting rid of overly vague functions like this.

Yeah, making the intent more explicit would be highly welcome.