linux-kernel - Re: [tip:x86/mm] x86/mm: Add support for early encryption/decryption of memory

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Message-ID: <e7914372-f8f4-c9eb-c262-f60b9e04b48f@intel.com>
Date:   Thu, 26 Oct 2017 07:08:00 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>, arnd@...db.de,
        aryabinin@...tuozzo.com, dvyukov@...gle.com, mingo@...nel.org,
        pbonzini@...hat.com, peterz@...radead.org,
        torvalds@...ux-foundation.org, toshi.kani@....com,
        matt@...eblueprint.co.uk, corbet@....net, hpa@...or.com,
        konrad.wilk@...cle.com, dyoung@...hat.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, riel@...hat.com, bp@...e.de,
        lwoodman@...hat.com, glider@...gle.com, luto@...nel.org,
        mst@...hat.com, brijesh.singh@....com, rkrcmar@...hat.com,
        bp@...en8.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mm: Add support for early encryption/decryption
 of memory

On 10/26/2017 06:05 AM, Tom Lendacky wrote:
>>>
>>> +static void __init __sme_early_enc_dec(resource_size_t paddr,
>>> +                       unsigned long size, bool enc)
>>> +{
>>> +    void *src, *dst;
>>> +    size_t len;
>>> +
>>> +    if (!sme_me_mask)
>>> +        return;
>>> +
>>> +    local_flush_tlb();
>>> +    wbinvd();
>>
>> What is this TLB flush for?  WBINVD is mentioned in "Volume 2, Section
>> 7.10.8", but TLB flushes are not.  Is it OK that this does not flush
>> global pages?
> 
> The local_flush_tlb() is not needed and can be removed. I had that in
> there from early development and testing and just missed removing it.
> I can queue up a patch to delete it and remove the ambiguity with this
> routine and the APM document.

Cool, I was just doing a little audit of those TLB flushes and this one
stuck out at me.  It would be great if it can be removed.