linux-kernel - Re: [PATCH v2] x86/efi: Safely enable unaccepted memory in UEFI

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Message-ID: <def9b0b5-b880-be99-fa95-b05d76a91824@intel.com>
Date:   Mon, 16 Jan 2023 13:22:45 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Gerd Hoffmann <kraxel@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dionna Glaze <dionnaglaze@...gle.com>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        x86@...nel.org, jiewen.yao@...el.com, devel@...2.groups.io,
        Ard Biescheuvel <ardb@...nel.org>,
        "Min M. Xu" <min.m.xu@...el.org>,
        James Bottomley <jejb@...ux.ibm.com>,
        Tom Lendacky <Thomas.Lendacky@....com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v2] x86/efi: Safely enable unaccepted memory in UEFI

On 1/16/23 02:56, Gerd Hoffmann wrote:
>> And we add this protocol to address very temporary problem: once
>> unaccepted memory support get upstream it is just a dead weight.
> Maybe, maybe not.  unaccepted memory support has a Kconfig switch after
> all.  If we figure in 3-5 years that all distros have enabled it anyway
> we can drop it again.  For the transition period it will surely be
> useful.

I agree with Kirill here.

Having unaccepted memory *AND* this firmware-driven feature really is
just implementing the same thing twice.

I'd much rather have the Kconfig option forced on for all guests that
*might* need unaccepted memory support than carry redundant implementations.

Also, _if_ we allow folks to turn the Kconfig off and get access to all
their memory, they might get used to that.  Removing this firmware
interface from the kernel in a few years could be viewed as a
regression.  Then, we'll be stuck with this forever.

In any case, the firmware side of things didn't seem like _that_ much
code.  So, I'm not protesting *that* strongly.  But, I also don't
believe for a second that this is going to be removed in 3-5 years.