linux-kernel - Re: [PATCH v4 04/19] x86/cea: Export per CPU array 'cea_exception

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: <c1481083-ee0d-4d58-aa07-01e43fec7c9f@zytor.com>
Date: Fri, 11 Apr 2025 09:16:33 -0700
From: Xin Li <xin@...or.com>
To: Dave Hansen <dave.hansen@...el.com>, Christoph Hellwig <hch@...radead.org>
Cc: pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        andrew.cooper3@...rix.com, luto@...nel.org, peterz@...radead.org,
        chao.gao@...el.com, xin3.li@...el.com
Subject: Re: [PATCH v4 04/19] x86/cea: Export per CPU array
 'cea_exception_stacks' for KVM to use

On 4/10/2025 7:18 AM, Dave Hansen wrote:
> On 4/10/25 01:53, Christoph Hellwig wrote:
>> On Fri, Mar 28, 2025 at 10:11:50AM -0700, Xin Li (Intel) wrote:
>>> The per CPU array 'cea_exception_stacks' points to per CPU stacks
>>> +/*
>>> + * FRED introduced new fields in the host-state area of the VMCS for
>>> + * stack levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively
>>> + * corresponding to per CPU stacks for #DB, NMI and #DF.  KVM must
>>> + * populate these each time a vCPU is loaded onto a CPU.
>>> + */
>>> +EXPORT_PER_CPU_SYMBOL(cea_exception_stacks);
>> Exporting data vs accessors for it is usually a bad idea.  Doing a
>> non-_GPl for such a very low level data struture is even worse.
> 
> Big ack on this.
> 
> I don't even see a single caller of __this_cpu_ist_top_va() that's
> remotely performance sensitive or that needs to be inline.
> 
> Just make the __this_cpu_ist_top/bottom_va() macros into real functions
> and export __this_cpu_ist_top_va(). It's going to be a pretty tiny
> function but I think that's tolerable.
> 

Right, that does make sense to me.