From: "Dionna Glaze" <dionnaglaze@google.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Ard Biesheuvel <ardb@kernel.org>,
Gerd Hoffmann <kraxel@redhat.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
x86@kernel.org, jiewen.yao@intel.com, devel@edk2.groups.io,
"Min M. Xu" <min.m.xu@intel.org>,
James Bottomley <jejb@linux.ibm.com>,
Tom Lendacky <Thomas.Lendacky@amd.com>,
Erdem Aktas <erdemaktas@google.com>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH v2] x86/efi: Safely enable unaccepted memory in UEFI
Date: Mon, 16 Jan 2023 11:43:15 -0800 [thread overview]
Message-ID: <CAAH4kHb6-6QkMnYbcQ6MyMkwSBUN-Q3CcM3fuiStdbbnSfJv1A@mail.gmail.com> (raw)
In-Reply-To: <20230116134246.soworigs56bz5v7o@box.shutemov.name>
> > I still don't understand why we need to support every imaginable
> > combination of firmware, bootloader and OS. Unaccepted memory only
> > exists on a special kind of virtual machine, which provides very
> > little added value unless you opt into the security and attestation
> > features, which are all heavily based on firmware protocols. So why
> > should care about a EFI-aware bootloader calling ExitBootServices()
> > and subsequently doing a legacy boot of Linux on such systems?
>
> Why break what works? Some users want it.
>
The users that want legacy boot features will not be broken, they'll
only get a safe view of the memory map. I don't think it's right to
choose unsafe behavior for a legacy setup.
> This patch adds complexity, breaks what works and the only upside will
> turn into a dead weight soon.
>
> There's alternative to add option to instruct firmware to accept all
> memory from VMM side. It will serve legacy OS that doesn't know about
> unaccepted memory and it is also can be use by latency-sensitive users
> later on (analog of qemu -mem-prealloc).
>
This means that users of a distro that has not enabled unaccepted
memory support cannot simply start a VM with the usual command, but
instead have to know a baroque extra flag to get access to all the
memory that they configured the machine (and for a CSP customer, paid
for). That's not a good experience.
With GCE at least, you can't (shouldn't) associate the boot feature
flag with a disk image because disks are mutable. If a customer
upgrades their kernel after initially starting their VM, they can't
remove the flag due to the way image annotations work.
All of this headache goes away by adopting a small patch to the kernel
that calls a 0-ary protocol interface and keeping safe acceptance
behavior in the firmware. I think Gerd is right here that we should
treat it as a transition feature that we can remove later.
> --
> Kiryl Shutsemau / Kirill A. Shutemov
--
-Dionna Glaze, PhD (she/her)
next prev parent reply other threads:[~2023-01-16 19:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-13 21:29 [PATCH v2] x86/efi: Safely enable unaccepted memory in UEFI Dionna Glaze
2023-01-13 22:20 ` Kirill A. Shutemov
2023-01-16 10:56 ` Gerd Hoffmann
2023-01-16 12:30 ` Kirill A. Shutemov
2023-01-16 13:11 ` Ard Biesheuvel
2023-01-16 13:42 ` Kirill A. Shutemov
2023-01-16 19:43 ` Dionna Glaze [this message]
2023-01-16 23:17 ` Kirill A. Shutemov
2023-01-17 10:24 ` Gerd Hoffmann
2023-01-17 16:45 ` Dionna Glaze
2023-01-18 7:51 ` [edk2-devel] " Gerd Hoffmann
2023-01-16 21:22 ` Dave Hansen
2023-01-16 22:46 ` Lendacky, Thomas
2023-01-18 15:09 ` Ard Biesheuvel
2023-01-18 15:40 ` Dave Hansen
2023-01-18 15:46 ` Ard Biesheuvel
2023-01-17 10:34 ` Gerd Hoffmann
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-list from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAAH4kHb6-6QkMnYbcQ6MyMkwSBUN-Q3CcM3fuiStdbbnSfJv1A@mail.gmail.com \
--to=devel@edk2.groups.io \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox