Re: [PATCH][4.17] EFI: don't convert memory marked for runtime use to ordinary RAM

From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"Volodymyr Babchuk" <volodymyr_babchuk@epam.com>,
	"Henry Wang" <Henry.Wang@arm.com>,
	"Bertrand Marquis" <Bertrand.Marquis@arm.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>
Subject: Re: [PATCH][4.17] EFI: don't convert memory marked for runtime use to ordinary RAM
Date: Sat, 8 Oct 2022 20:08:03 +0100	[thread overview]
Message-ID: <a957dfbe-c4c4-c8cc-93c5-616a44fe1797@xen.org> (raw)
In-Reply-To: <82963a1c-3301-72ff-e995-77c30ec5a64b@suse.com>

Hi Jan,

On 06/10/2022 15:11, Jan Beulich wrote:
>> ... the space cannot become ordinary RAM, then such a precaution
>> wouldn't be necessary. After all hiding EfiACPIReclaimMemory from
>> Dom0 just because it can't be mapped WB wouldn't be very nice
>> either. I guess I'll submit v2 with this part of the change left
>> as it was.
> 
> And while already in the process of committing the patch I came to
> realize that if the WB conditional isn't supposed to move, isn't
> the change done for Arm then wrong as well? Shouldn't it then be
> 
>          if ( !(desc_ptr->Attribute & EFI_MEMORY_RUNTIME) &&
>               (desc_ptr->Attribute & EFI_MEMORY_WB) &&
>               (desc_ptr->Type == EfiConventionalMemory ||
>               ...
> 
> leaving the EfiACPIReclaimMemory case entirely unaffected by the
> change?

IIUC, the concern is the region EfiACPIReclaimMemory could have the 
attribute EFI_MEMORY_RUNTIME. Is that correct?

Given that the memory is reclaimable, I am not sure why it can also have 
this atribute set (to me it means the opposite). But I guess for 
hardening purpose it would be better to use the version you just suggested.

Bertrand, Stefano, what do you think?

Cheers,

-- 
Julien Grall