linux-kernel - Re: [PATCHv2 1/3] x86, ptdump: Add section for EFI runtime services

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Date:	Tue, 28 Oct 2014 21:13:42 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Mathias Krause <minipli@...glemail.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	x86-ml <x86@...nel.org>, Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCHv2 1/3] x86, ptdump: Add section for EFI runtime services

On Tue, Oct 28, 2014 at 08:48:23PM +0100, Mathias Krause wrote:
> I tried so too but failed early as well. I tried putting the EFI
> virtual mappings not in trampoline_pgd[511] but trampoline_pgd[510].
> However, that didn't work out. I got page faults when trying to invoke
> EFI functions, as, apparently, efi.systab was only mapped in the EFI
> page table but not the kernel's page table -- at least not at the same
> address. So when efi_call_virt() tries to dereference
> efi.systab->runtime->f, it just traps.
> I tried to hack around that by fiddling with get_systab_virt_addr() to
> make it point to the direct mapping for the phys_addr but failed on
> the first few attempts to get the math right. Then I noticed it was
> way to late to hack EFI code and fell asleep. Next day I just gave up
> and 'git reset --hard HEAD'. :(

I know exactly what you mean. The nasty thing about it is, debugging
this is not trivial as once you switch to another page table, you don't
have a #PF handler and the guest triple-faults. All of the above issues
I've encountered already while hacking on the current code :-) *Cringe*

I want to do experimentation with tracing page faults in KVM with the
nested PF handling in hw turned off so that I can see all #PFs. Maybe
that'll tell me something more, we'll see.

> Debian's version of qemu + OVMF works fine here. Probably slightly
> outdated but still good enough for testing EFI stuff ;)

Yeah, Paolo fixed it already:

https://lkml.kernel.org/r/1414420306-2771-2-git-send-email-pbonzini@redhat.com

I think we want to keep qemu+kvm functioning :-)

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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