RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi_pgd

From: "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@intel.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"x86@kernel.org" <x86@kernel.org>, "bp@alien8.de" <bp@alien8.de>,
	"marc.zyngier@arm.com" <marc.zyngier@arm.com>,
	"eric.snowberg@oracle.com" <eric.snowberg@oracle.com>,
	"hdegoede@redhat.com" <hdegoede@redhat.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"arend.vanspriel@broadcom.com" <arend.vanspriel@broadcom.com>,
	"julien.thierry@arm.com" <julien.thierry@arm.com>,
	"bhsharma@redhat.com" <bhsharma@redhat.com>,
	"jonathanh@nvidia.com" <jonathanh@nvidia.com>,
	"joe@perches.com" <joe@perches.com>,
	"matt@codeblueprint.co.uk" <matt@codeblueprint.co.uk>,
	"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
	"natechancellor@gmail.com" <natechancellor@gmail.com>,
	"luto@kernel.org" <luto@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"sedat.dilek@gmail.com" <sedat.dilek@gmail.com>,
	"zhuyifei1999@gmail.com" <zhuyifei1999@gmail.com>,
	"linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi_pgd
Date: Fri, 21 Dec 2018 17:52:52 +0000	[thread overview]
Message-ID: <FFF73D592F13FD46B8700F0A279B802F48606B36@ORSMSX114.amr.corp.intel.com> (raw)
In-Reply-To: <CAKv+Gu99VdPero0yrXiaByURyp1idYE948Qi4j1eqY0ENCrF5A@mail.gmail.com>

> > > For the short term, could we simply make your changes dependent on
> > > efi != old_map? That gives us some time to fix the old_map case properly.
> >
> > Yes, I think we could and it should work but I hesitated to propose it
> > because (as you already noted) it's a short term fix and not the right fix.
> >
> 
> What is the status here?

Making the unmapping code conditional on !old_map is ready and I will send it out.
I am working on unmapping boot services code/data when old_map is enabled 
and ran into issues with memblock and direct mapping in kernel. Will post those details 
in a separate thread.

> 
> > Alternatively, we could also evaluate if we need to support efi=old_map case
> going further.
> > I thought dropping it would be a bad idea because it changes kernel
> > user visible interface (because it's a kernel command line argument) and never
> brought it up.
> > Not sure what Thomas, Ingo or Linus might think about dropping a
> > kernel command line argument.
> >
> 
> Dropping a command line argument is not a problem in itself, unless anyone is
> actively using it :-)
> 
> As far as I can tell, the SGI x86 UV platforms still rely on this, so we're stuck with
> it for the foreseeable future.

Thanks (also Boris) for the info. Makes sense why we need efi=old_map.

> 
> This means we need a fixes that makes your unmapping code conditional on
> !old_memmap. Do you have an ETA for that?

Sure! I will do some more testing and if it works as expected, will send it before this Sunday.

Regards,
Sai