linux-kernel - Re: [PATCH v5 28/32] x86/mm, kexec: Allow kexec to be used with SME

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Date:   Fri, 19 May 2017 16:38:07 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 28/32] x86/mm, kexec: Allow kexec to be used with SME

On 5/19/2017 4:28 PM, Borislav Petkov wrote:
> On Fri, May 19, 2017 at 04:07:24PM -0500, Tom Lendacky wrote:
>> As long as those never change from static inline everything will be
>> fine. I can change it, but I really like how it explicitly indicates
>
> I know what you want to do. But you're practically defining a helper
> which contains two arbitrary instructions which probably no one else
> will need.
>
> So how about we simplify this function even more. We don't need to pay
> attention to kexec being in progress because we're halting anyway so who
> cares how fast we halt.
>
> Might have to state that in the comment below though, instead of what's
> there now.
>
> And for the exact same moot reason, we don't need to look at SME CPUID
> feature - we can just as well WBINVD unconditionally.
>
> void stop_this_cpu(void *dummy)
> {
>         local_irq_disable();
>         /*
>          * Remove this CPU:
>          */
>         set_cpu_online(smp_processor_id(), false);
>         disable_local_APIC();
>         mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
>
>         for (;;) {
>                 /*
>                  * If we are performing a kexec and the processor supports
>                  * SME then we need to clear out cache information before
>                  * halting. With kexec, going from SME inactive to SME active
>                  * requires clearing cache entries so that addresses without
>                  * the encryption bit set don't corrupt the same physical
>                  * address that has the encryption bit set when caches are
>                  * flushed. Perform a wbinvd followed by a halt to achieve
>                  * this.
>                  */
>                 asm volatile("wbinvd; hlt" ::: "memory");
>         }
> }
>
> How's that?

I can live with that!

Thanks,
Tom

>