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Message-ID: <20230116123057.wvr6rz7y3ubgcm5z@box.shutemov.name>
Date: Mon, 16 Jan 2023 15:30:57 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
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 Mon, Jan 16, 2023 at 11:56:48AM +0100, Gerd Hoffmann wrote:
> On Sat, Jan 14, 2023 at 01:20:24AM +0300, Kirill A. Shutemov wrote:
> > On Fri, Jan 13, 2023 at 09:29:26PM +0000, Dionna Glaze wrote:
> > > This patch depends on Kirill A. Shutemov's series
> > >
> > > [PATCHv8 00/14] mm, x86/cc: Implement support for unaccepted memory
> > >
> > > The UEFI v2.9 specification includes a new memory type to be used in
> > > environments where the OS must accept memory that is provided from its
> > > host. Before the introduction of this memory type, all memory was
> > > accepted eagerly in the firmware. In order for the firmware to safely
> > > stop accepting memory on the OS's behalf, the OS must affirmatively
> > > indicate support to the firmware.
> >
> > I think it is a bad idea.
> >
> > This approach breaks use case with a bootloader between BIOS and OS.
> > As the bootloader does ExitBootServices() it has to make the call on
> > behalf of OS when it has no idea if the OS supports unaccepted.
>
> Nothing breaks, it'll error on the safe side. If the protocol callback
> is not called the firmware will simply accept all memory. The guest OS
> will only see unaccepted memory if it explicitly asked for it (assuming
> the firmware wants know to support both cases, of course the firmware
> could also enforce the one or the other and just not offer the
> protocol).
How bootloader suppose to know if OS will ask for unaccepted memory?
It can't. It means the use-case with bootloader cannot ever use
unaccepted memory. That's broken design.
--
Kiryl Shutsemau / Kirill A. Shutemov
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