Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Andrew Morton]

On Thu, 03 Aug 2006 01:58:32 -0700
Zachary Amsden <zach@vmware.com> wrote:

> Add a bootparameter to reserve high linear address space for hypervisors.
> This is necessary to allow dynamically loaded hypervisor modules, which
> might not happen until userspace is already running, and also provides a
> useful tool to benchmark the performance impact of reduced lowmem address
> space.

Andi has gone and rotorooted the x86 boot parameter handling in there. 
This patch now looks like this:


From: Zachary Amsden <zach@vmware.com>

Add a boot parameter to reserve high linear address space for hypervisors. 
This is necessary to allow dynamically loaded hypervisor modules, which might
not happen until userspace is already running, and also provides a useful tool
to benchmark the performance impact of reduced lowmem address space.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 Documentation/kernel-parameters.txt |    5 +++++
 arch/i386/kernel/setup.c            |   24 ++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff -puN arch/i386/kernel/setup.c~x86-add-a-bootparameter-to-reserve-high-linear-address-space arch/i386/kernel/setup.c
--- a/arch/i386/kernel/setup.c~x86-add-a-bootparameter-to-reserve-high-linear-address-space
+++ a/arch/i386/kernel/setup.c
@@ -149,6 +149,12 @@ static char command_line[COMMAND_LINE_SI
 
 unsigned char __initdata boot_params[PARAM_SIZE];
 
+static int __init setup_reservetop(char *s)
+{
+	return 1;
+}
+__setup("reservetop", setup_reservetop);
+
 static struct resource data_resource = {
 	.name	= "Kernel data",
 	.start	= 0,
@@ -814,6 +820,24 @@ static int __init parse_vmalloc(char *ar
 early_param("vmalloc", parse_vmalloc);
 
 /*
+ * reservetop=size reserves a hole at the top of the kernel address space which
+ * a hypervisor can load into later.  Needed for dynamically loaded hypervisors,
+ * so relocating the fixmap can be done before paging initialization.
+ */
+static int __init parse_reservetop(char *arg)
+{
+	unsigned long address;
+
+	if (!arg)
+		return -EINVAL;
+
+	address = memparse(arg, &arg);
+	reserve_top_address(address);
+	return 0;
+}
+early_param("reservetop", parse_reservetop);
+
+/*
  * Callback for efi_memory_walk.
  */
 static int __init
diff -puN Documentation/kernel-parameters.txt~x86-add-a-bootparameter-to-reserve-high-linear-address-space Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt~x86-add-a-bootparameter-to-reserve-high-linear-address-space
+++ a/Documentation/kernel-parameters.txt
@@ -1357,6 +1357,11 @@ running once the system is up.
 
 	reserve=	[KNL,BUGS] Force the kernel to ignore some iomem area
 
+	reservetop=	[IA-32]
+			Format: nn[KMG]
+			Reserves a hole at the top of the kernel virtual
+			address space.
+
 	resume=		[SWSUSP]
 			Specify the partition device for software suspend
 
_

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Zachary Amsden]

Andrew Morton wrote:
> On Thu, 03 Aug 2006 01:58:32 -0700
> Zachary Amsden <zach@vmware.com> wrote:
>
>   
>> Add a bootparameter to reserve high linear address space for hypervisors.
>> This is necessary to allow dynamically loaded hypervisor modules, which
>> might not happen until userspace is already running, and also provides a
>> useful tool to benchmark the performance impact of reduced lowmem address
>> space.
>>     
>
> Andi has gone and rotorooted the x86 boot parameter handling in there. 
> This patch now looks like this:
>   

The rototilled patch looks great.  Acked.

Zach

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Rusty Russell]

On Sat, 2006-08-05 at 14:58 -0700, Andrew Morton wrote:
> On Thu, 03 Aug 2006 01:58:32 -0700
> Zachary Amsden <zach@vmware.com> wrote:
> 
> > Add a bootparameter to reserve high linear address space for hypervisors.
> > This is necessary to allow dynamically loaded hypervisor modules, which
> > might not happen until userspace is already running, and also provides a
> > useful tool to benchmark the performance impact of reduced lowmem address
> > space.
> 
> Andi has gone and rotorooted the x86 boot parameter handling in there. 

That was me, via Andi, but yep:

> diff -puN arch/i386/kernel/setup.c~x86-add-a-bootparameter-to-reserve-high-linear-address-space arch/i386/kernel/setup.c
> --- a/arch/i386/kernel/setup.c~x86-add-a-bootparameter-to-reserve-high-linear-address-space
> +++ a/arch/i386/kernel/setup.c
> @@ -149,6 +149,12 @@ static char command_line[COMMAND_LINE_SI
>  
>  unsigned char __initdata boot_params[PARAM_SIZE];
>  
> +static int __init setup_reservetop(char *s)
> +{
> +	return 1;
> +}
> +__setup("reservetop", setup_reservetop);
> +
>  static struct resource data_resource = {
>  	.name	= "Kernel data",
>  	.start	= 0,

Please remove this hunk: it's now junk.

Cheers,
Rusty.
-- 
Help! Save Australia from the worst of the DMCA: http://linux.org.au/law

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Pavel Machek]

Hi!

> Add a bootparameter to reserve high linear address space for hypervisors.
> This is necessary to allow dynamically loaded hypervisor modules, which

Dynamically loaded hypervisor? Do we really want to support that?

							Pavel
-- 
Thanks for all the (sleeping) penguins.

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Pavel Machek]

Hi!

> Add a bootparameter to reserve high linear address space for hypervisors.
> This is necessary to allow dynamically loaded hypervisor modules, which

Dynamically loaded hypervisor? Do we really want to support that?

							Pavel
-- 
Thanks for all the (sleeping) penguins.

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Andi Kleen]

On Thursday 01 January 1970 01:15, Pavel Machek wrote:
> Hi!
> 
> > Add a bootparameter to reserve high linear address space for hypervisors.
> > This is necessary to allow dynamically loaded hypervisor modules, which
> 
> Dynamically loaded hypervisor? Do we really want to support that?

I hope so. IMHO letting Linux boot first and then the Hypervisor is 
a better design than the other way round which requires a lot of duplicated code.

-Andi

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Jeremy Fitzhardinge]

On 12/31/1969 04:15 PM, Pavel Machek wrote:
> Dynamically loaded hypervisor? Do we really want to support that?
>   

(Missed this because your datestamp was 1969...)

The idea was that you could boot a guest under VMWare fully virtualized
then switch it to a VMI guest by loading a module.  I don't think it
ever worked out - the transition was too trick to get right (especially
applying all the pvops patching to a live system).

    J

Re: [patch 7/8] Add a bootparameter to reserve high linear address space.

[Pavel Machek]

Hi!

> Add a bootparameter to reserve high linear address space for hypervisors.
> This is necessary to allow dynamically loaded hypervisor modules, which

Dynamically loaded hypervisor? Do we really want to support that?

							Pavel
-- 
Thanks for all the (sleeping) penguins.