linux-kernel - Re: [PATCH v3 1/6] x86/sme: Use percpu boolean to control wbinvd during kexec

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: <065b56f9743a18aa1866153a146a18b46df9ef8f.camel@intel.com>
Date: Fri, 27 Jun 2025 00:37:45 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Hansen, Dave" <dave.hansen@...el.com>, "Edgecombe, Rick P"
	<rick.p.edgecombe@...el.com>, "bp@...en8.de" <bp@...en8.de>,
	"peterz@...radead.org" <peterz@...radead.org>, "hpa@...or.com"
	<hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "thomas.lendacky@....com" <thomas.lendacky@....com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "x86@...nel.org"
	<x86@...nel.org>, "sagis@...gle.com" <sagis@...gle.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "kirill.shutemov@...ux.intel.com"
	<kirill.shutemov@...ux.intel.com>, "Williams, Dan J"
	<dan.j.williams@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "ashish.kalra@....com" <ashish.kalra@....com>,
	"nik.borisov@...e.com" <nik.borisov@...e.com>
Subject: Re: [PATCH v3 1/6] x86/sme: Use percpu boolean to control wbinvd
 during kexec


(I'll address all wording comments, as always.)

> > Today the first WBINVD in the stop_this_cpu() is performed when SME is
> > *supported* by the platform, and the second WBINVD is done in
> > relocate_kernel() when SME is *activated* by the kernel.  Make things
> > simple by changing to do the second WBINVD when the platform supports
> > SME.  This allows the kernel to simply turn on this percpu boolean when
> > bringing up a CPU by checking whether the platform supports SME.
> 
> Since the race is related to stop_this_cpu() it doesn't affect it. But it does
> mean that the bring up CPU may not flush the cache if takes a kdump kexec before
> the per-cpu var is set? Of course the existing logic doesn't trigger until
> cpuinfo_x86 is populated. What is the consequence?

See another reply.

> 
> Arguably the supported/enabled part could be moved to a separate earlier patch.
> The code change would just get immediately replaced, but the benefit would be
> that a bisect would show which part of the change was responsible.

I am not a fan of splitting the new variable and the user into different
patches, as long as the patch isn't too big to review.  You need to review
them together anyway I think, so arguably putting them together is easier to
review.