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: <2e843e28-2836-910e-bcd8-f35872adf21a@suse.com>
Date:   Fri, 30 Sep 2022 15:11:07 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 08/10] x86/mtrr: let cache_aps_delayed_init replace
 mtrr_aps_delayed_init

On 30.09.22 13:55, Borislav Petkov wrote:
> On Thu, Sep 29, 2022 at 10:26:59AM +0200, Juergen Gross wrote:
>> So right now I'm inclined to be better on the safe side by not adding any
>> cpu hotplug hook, but to use just the same "delayed AP init" flag as today,
>> just renaming it. This would leave the delayed MTRR/PAT init in place for
>> resume and kexec cases, but deferring the MTRR/PAT cleanup due to this
>> potential issue seems not appropriate, as the cleanup isn't changing the
>> behavior here.
> 
> Ok, what's wrong with adding a special hotplug level just for that thing
> and running it very early? Practically pretty much where it was in time,
> in identify_secondary_cpu()?

Yes, this can be done. It would practically have to be the first one just
after CPUHP_BRINGUP_CPU.

The question is whether we really want to call the MTRR/PAT initialization
on hotplugged cpus only after enabling interrupts. Note that the callbacks
are activated only at the end of start_secondary(), while today MTRR/PAT
initialization is called some time earlier by:

   start_secondary()
     smp_callin()
       smp_store_cpu_info()
         identify_secondary_cpu()
           mtrr_ap_init()

I don't think this is a real problem, but I wanted to mention it.

The next question would be, why MTRR/PAT init should be special (meaning:
why are all the other functions called that early not realized via
callbacks)? Is it just because of the special handling during boot/resume?

It might be worth a discussion whether there shouldn't be a special group
of callbacks activated BEFORE interrupts are being enabled.

> Having a special one is warranted, as you explain, I'd say.

Thanks. I'll write a patch for that.


Juergen


Download attachment "OpenPGP_0xB0DE9DD628BF132F.asc" of type "application/pgp-keys" (3099 bytes)

Download attachment "OpenPGP_signature" of type "application/pgp-signature" (496 bytes)

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ