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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Alexander van Heukelum <heukelum@fastmail.fm>
Cc: Mark McLoughlin <markmc@redhat.com>,
	Alexander van Heukelum <heukelum@mailshack.com>,
	Ingo Molnar <mingo@elte.hu>, Ian Campbell <ijc@hellion.org.uk>,
	"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@suse.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2
Date: Tue, 04 Mar 2008 09:11:33 -0800	[thread overview]
Message-ID: <47CD82C5.8060605@goop.org> (raw)
In-Reply-To: <1204649476.5048.1240509149@webmail.messagingengine.com>

Alexander van Heukelum wrote:
> On Tue, 04 Mar 2008 07:18:48 -0800, "Jeremy Fitzhardinge"
> <jeremy@goop.org> said:
>   
>> Mark McLoughlin wrote:
>>     
>>> This is a bit magic, is it worth splitting it out as something like
>>> is_paravirt_environment() ?
>>>   
>>>       
>> Yes, is_paravirt() already exists for this purpose.
>>     
>
> Hi,
>
> If it exists, it is well-hidden. A grep for is_paravirt on the testing
> tree turns up nothing. Did you get the name right?
>   

Nope.  paravirt_enabled().

>> The code looking at the boot params will only work if we actually booted 
>> via the paravirt Linux boot protocol, which Xen doesn't at present.
>>     
>
> I chose to code it exactly this way, because it is what is used in
> head_32.S to choose how to start the kernel. Or is this code not
> executed at all?
>   

No, this isn't executed when booting under Xen.  Xen is a bit magic, and 
has its own kernel entrypoint which the domain builder finds via 
Xen-specific ELF notes on the vmlinux.  We plan to move to booting via 
this path at some point.

> [excerpt form head_32.S]
>         cmpw $0x207, pa(boot_params + BP_version)
>         jb default_entry
>
>         /* Paravirt-compatible boot parameters.  Look to see what
>         architecture
>                 we're booting under. */
>         movl pa(boot_params + BP_hardware_subarch), %eax
>         cmpl $num_subarch_entries, %eax
>         jae bad_subarch
>
>         movl pa(subarch_entries)(,%eax,4), %eax
>         subl $__PAGE_OFFSET, %eax
>         jmp *%eax
> [and]
> subarch_entries:
>         .long default_entry             /* normal x86/PC */
>         .long lguest_entry              /* lguest hypervisor */
>         .long xen_entry                 /* Xen hypervisor */
> num_subarch_entries = (. - subarch_entries) / 4
> [end]
>
> If this is indeed not executed, is there a way to detect whether
> we can expect the environment to behave like a normal pc in terms
> of magic addresses, bios areas, isa reserved address space and so
> on?
>   

Just because something is paravirtualized and uses a non-PC 
hardware_subarch doesn't mean this stuff isn't present.  Even the 
paravirt_enabled() test isn't accurate, because the environment may 
still choose to emulate these things (or in the Xen dom0 case, it may 
directly expose the real hardware).

    J

  parent reply	other threads:[~2008-03-04 17:17 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-24 17:46 [PATCH] Fix alignment of early reservation for EBDA Alexander van Heukelum
2008-02-24 19:27 ` Andi Kleen
2008-02-24 19:41 ` Ingo Molnar
2008-02-24 20:53   ` Alexander van Heukelum
2008-02-25  2:18 ` H. Peter Anvin
2008-02-25 16:54   ` Alexander van Heukelum
2008-02-25 17:01     ` Ingo Molnar
2008-02-25 18:07       ` [PATCH] reserve_early end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-25 18:13         ` H. Peter Anvin
2008-02-25 19:46           ` Alexander van Heukelum
2008-02-25 21:17             ` H. Peter Anvin
2008-02-26  9:30             ` Ingo Molnar
2008-02-27 14:26               ` Andi Kleen
2008-02-27 14:38               ` [PATCH] reserve_early end-of-conventional-memory to 1MB II - some numbers to put it into perspective Andi Kleen
2008-02-27 16:44                 ` H. Peter Anvin
2008-02-27 20:01                 ` Alexander van Heukelum
2008-02-28 13:13         ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Alexander van Heukelum
2008-02-28 13:28           ` [RFC] use realmode code to reserve end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-28 21:12             ` Ian Campbell
2008-02-28 21:14               ` H. Peter Anvin
2008-02-28 23:16                 ` Ian Campbell
2008-02-29 20:00                   ` Ingo Molnar
2008-03-04 11:41                   ` Mark McLoughlin
2008-03-04 14:33                     ` Ingo Molnar
2008-03-04 15:12                       ` Ian Campbell
2008-03-04 15:13                       ` Jeremy Fitzhardinge
2008-03-04 15:25                         ` Ingo Molnar
2008-03-04 16:02                           ` Jeremy Fitzhardinge
2008-03-04 16:15                             ` Ingo Molnar
2008-03-04 16:15                       ` Mark McLoughlin
2008-03-04 16:23                         ` Ingo Molnar
2008-03-04 17:44                   ` Jeremy Fitzhardinge
2008-03-05 15:59                   ` Eduardo Habkost
2008-03-05 16:08                     ` H. Peter Anvin
2008-03-05 16:53                       ` Eduardo Habkost
2008-03-05 17:28                         ` H. Peter Anvin
2008-03-05 17:28                           ` Jeremy Fitzhardinge
2008-03-05 17:38                             ` H. Peter Anvin
2008-03-05 16:38                     ` Jeremy Fitzhardinge
2008-03-05 17:27                       ` H. Peter Anvin
2008-02-28 21:09           ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Ian Campbell
2008-02-29 11:49             ` Alexander van Heukelum
2008-02-29 17:14               ` Mark McLoughlin
2008-02-29 18:38                 ` Alexander van Heukelum
2008-02-29 18:44                   ` H. Peter Anvin
2008-02-29 18:56                     ` Alexander van Heukelum
2008-02-29 22:06                   ` Mark McLoughlin
2008-02-29 22:26                     ` Alexander van Heukelum
2008-03-01 16:09                     ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Alexander van Heukelum
2008-03-01 16:12                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 64-bit add-on Alexander van Heukelum
2008-03-04 11:44                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Mark McLoughlin
2008-03-04 13:31                         ` Alexander van Heukelum
2008-03-04 14:49                         ` Ingo Molnar
2008-03-04 15:16                           ` Mark McLoughlin
2008-03-04 15:24                             ` Ingo Molnar
2008-03-04 15:18                         ` Jeremy Fitzhardinge
2008-03-04 16:51                           ` Alexander van Heukelum
2008-03-04 17:05                             ` H. Peter Anvin
2008-03-04 17:11                             ` Jeremy Fitzhardinge [this message]
2008-03-04 18:57                               ` [PATCH] reserve end-of-conventional-memory to 1MB, 32-bit, use paravirt_enabled Alexander van Heukelum
2008-03-04 19:12                                 ` [PATCH] reserve end-of-conventional-memory to 1MB, 64-bit, " Alexander van Heukelum
2008-02-27 14:25     ` [PATCH] Fix alignment of early reservation for EBDA Andi Kleen

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