linux-kernel - Re: CMA enhancement - non-default areas in x86

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Message-ID: <20200513083343.GA772573@kroah.com>
Date:   Wed, 13 May 2020 10:33:43 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     "Ravich, Leonid" <Leonid.Ravich@...l.com>
Cc:     "Idgar, Or" <Or.Idgar@...l.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: CMA enhancement - non-default areas in x86

A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Wed, May 13, 2020 at 08:29:16AM +0000, Ravich, Leonid wrote:
> PCIe NTB 
> Documentation/driver-api/ntb.rst

> 1) Basically PCI bridge between to root complex / PCI switches 
> 2) using out of OS memory is one solution but then this memory is
> Limited for usage by other stack, ex: get_user_pages on this memory will fail, 
> Therefore attempting to use it for block layer with (o_direct) will fail. 
>  
> Acutely any generic stack which attempts to "pin" this memory will fail.

So why isn't the BIOS/UEFI properly reserving this from the general
operating system's pages so that the driver knows to use them instead?

Is UEFI wrong here about these being valid memory ranges for general
use?  If so, why not fix that?  If not, how in the world is the OS
supposed to know these memory ranges are _not_ for general use?  I feel
like there is something missing here...

thanks,

greg k-h