linux-kernel - Re: [PATCH 0/3] Resolve problems with kexec identity mapping

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Message-ID: <20240703154301.GEZoVxhREtHjk0vtaL@fat_crate.local>
Date: Wed, 3 Jul 2024 18:14:41 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Steve Wahl <steve.wahl@....com>, Ashish Kalra <ashish.kalra@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Pavin Joseph <me@...injoseph.com>,
	Eric Hagberg <ehagberg@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, Sarah Brofeldt <srhb@....dk>,
	Russ Anderson <rja@....com>, Dimitri Sivanich <sivanich@....com>,
	Hou Wenlong <houwenlong.hwl@...group.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Yuntao Wang <ytcoode@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Joerg Roedel <jroedel@...e.de>,
	Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/3] Resolve problems with kexec identity mapping

On Tue, Jul 02, 2024 at 08:32:22PM +0200, Ard Biesheuvel wrote:
> For kexec on a 64-bit system, I would expect the high-level support
> code to be capable of simply mapping all of DRAM 1:1, rather than
> playing these games with #PF handlers and on-demand mapping.

Yeah, apparently we can't do that on SGI, as Steve said.

I like the aspect that the #PF handler won't fire in the first kernel because
of EFI mapping all RAM. That's good.

So we could try to wire in a #PF handler in stage1, see below.

Steve, I don't have a good idea how to test that. Maybe some of those
reporters you were talking about, would be willing to...

---
diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index d100284bbef4..a258587c8949 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -32,6 +32,7 @@ void load_stage1_idt(void)
 {
 	boot_idt_desc.address = (unsigned long)boot_idt;
 
+	set_idt_entry(X86_TRAP_PF, boot_page_fault);
 
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
 		set_idt_entry(X86_TRAP_VC, boot_stage1_vc);

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette