From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124])
 by mx.groups.io with SMTP id smtpd.web11.11977.1683710285688067407
 for <devel@edk2.groups.io>;
 Wed, 10 May 2023 02:18:05 -0700
Authentication-Results: mx.groups.io;
 dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=fsTbkla0;
 spf=pass (domain: redhat.com, ip: 170.10.133.124, mailfrom: kraxel@redhat.com)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
	s=mimecast20190719; t=1683710284;
	h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
	 to:to:cc:cc:mime-version:mime-version:content-type:content-type:
	 in-reply-to:in-reply-to:references:references;
	bh=Y7Vbsgrso02ZfXr3vSluvUOYF/O90rOn6XqauRqIJPI=;
	b=fsTbkla0nHUAXjjv7jnRnjO/49G87JD8eWtPNugvKs39QTeMw/eUVWG68Vq9eJdqsBLnMZ
	EmB8kq9P4Kuiol3b2lkqz0By/vInplGVZvKIUoHrb0XSDMJDWTwUzva1GPUjcRDQ0Z2JGr
	6IhZKrFA9MmSGGtRS2gIciTGOLF77RU=
Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com
 [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS
 (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 us-mta-644-RXeST-LpPYWQQoeH2-MkNA-1; Wed, 10 May 2023 05:17:59 -0400
X-MC-Unique: RXeST-LpPYWQQoeH2-MkNA-1
Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6])
	(using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A5A10885627;
	Wed, 10 May 2023 09:17:58 +0000 (UTC)
Received: from sirius.home.kraxel.org (unknown [10.39.192.90])
	by smtp.corp.redhat.com (Postfix) with ESMTPS id 593D02166B26;
	Wed, 10 May 2023 09:17:58 +0000 (UTC)
Received: by sirius.home.kraxel.org (Postfix, from userid 1000)
	id 495E518003AB; Wed, 10 May 2023 11:17:55 +0200 (CEST)
Date: Wed, 10 May 2023 11:17:55 +0200
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: devel@edk2.groups.io, pedro.falcato@gmail.com
Cc: Andrew Fish <afish@apple.com>, 
	"Kinney, Michael D" <michael.d.kinney@intel.com>, Ray Ni <ray.ni@intel.com>, Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [edk2-devel] Side effects of enabling PML5 in EFI
Message-ID: <pitmz4if6srumff322u264l2hkr534ictq3zu2sepetoj7khch@6vcncx3jvl73>
References: <CAKbZUD346-0qU2E2dVXY7M9ev-GGfU=9OYFc8DwE53ndHyzOiw@mail.gmail.com>
MIME-Version: 1.0
In-Reply-To: <CAKbZUD346-0qU2E2dVXY7M9ev-GGfU=9OYFc8DwE53ndHyzOiw@mail.gmail.com>
X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6
X-Mimecast-Spam-Score: 0
X-Mimecast-Originator: redhat.com
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Tue, May 09, 2023 at 06:24:03PM +0100, Pedro Falcato wrote:
> Hi all,
> 
> (+CC people vaguely related to the EFI spec, the PML5 implementation
> and kernel EFI boot code)
> 
> As a result of the latest 5-level paging patches, I've been looking
> into how tiano supports PML5.
> This raised a question: Doesn't enabling PML5 in-firmware break
> compatibility with non-PML5-aware bootloaders and kernels?

kernels yes, bootloaders probably not (unless the bootloader not the
kernel calls exitbootservices).

> So, how is any of this supposed to work?

edk2 is relatively late to the party, so with everybody else supporting
5-level paging already it might not be much of an issue in practice even
though there is no compatibility handling (I know of) in edk2.

When running your operating system museum in virtual machines you have
the option to just turn off 5-level paging support in the virtual cpu.

take care,
  Gerd