Re: [Xen-devel] [PATCH] xen/arm: warn if dom0_mem is not specified

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 21 Feb 2017, Julien Grall wrote:
> Hi Stefano,
> 
> On 21/02/17 17:26, Stefano Stabellini wrote:
> > On Tue, 21 Feb 2017, Wei Liu wrote:
> > > On Mon, Feb 20, 2017 at 10:22:06AM -0800, Stefano Stabellini wrote:
> > > > The default dom0_mem is 128M which is not sufficient to boot a Ubuntu
> > > > based Dom0. It is not clear what a better default value could be.
> > > > 
> > > > Instead, loudly warn the user when dom0_mem is unspecified and wait 3
> > > > secs. Then use 512M.
> > > > 
> > > > Update the docs to specify that dom0_mem is required on ARM. (The
> > > > current xen-command-line document does not actually reflect the current
> > > > behavior of dom0_mem on ARM correctly.)
> > > > 
> > > > Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > > ---
> > > > Changes in v3:
> > > > - update docs
> > > > ---
> > > >  docs/misc/xen-command-line.markdown |  8 +++++++-
> > > >  xen/arch/arm/domain_build.c         | 22 +++++++++++++++++-----
> > > >  2 files changed, 24 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/docs/misc/xen-command-line.markdown
> > > > b/docs/misc/xen-command-line.markdown
> > > > index a11fdf9..c0106fb 100644
> > > > --- a/docs/misc/xen-command-line.markdown
> > > > +++ b/docs/misc/xen-command-line.markdown
> > > > @@ -603,7 +603,13 @@ For example, with `dom0_max_vcpus=4-8`:
> > > >  >      8    |  8
> > > >  >     10    |  8
> > > > 
> > > > -### dom0\_mem
> > > > +### dom0\_mem (ARM)
> > > > +> `= <size>`
> > > > +
> > > > +Set the amount of memory for the initial domain (dom0). It must be
> > > > +greater than zero. This parameter is required.
> > > > +
> > > > +### dom0\_mem (x86)
> > > >  > `= List of ( min:<size> | max:<size> | <size> )`
> > > > 
> > > >  Set the amount of memory for the initial domain (dom0). If a size is
> > > > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > > > index c97a1f5..db7471f 100644
> > > > --- a/xen/arch/arm/domain_build.c
> > > > +++ b/xen/arch/arm/domain_build.c
> > > > @@ -1,4 +1,5 @@
> > > >  #include <xen/config.h>
> > > > +#include <xen/delay.h>
> > > >  #include <xen/init.h>
> > > >  #include <xen/compile.h>
> > > >  #include <xen/lib.h>
> > > > @@ -31,14 +32,11 @@ integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
> > > > 
> > > >  int dom0_11_mapping = 1;
> > > > 
> > > > -#define DOM0_MEM_DEFAULT 0x8000000 /* 128 MiB */
> > > > -static u64 __initdata dom0_mem = DOM0_MEM_DEFAULT;
> > > > +static u64 __initdata dom0_mem;
> > > > 
> > > >  static void __init parse_dom0_mem(const char *s)
> > > >  {
> > > >      dom0_mem = parse_size_and_unit(s, &s);
> > > > -    if ( dom0_mem == 0 )
> > > > -        dom0_mem = DOM0_MEM_DEFAULT;
> > > >  }
> > > >  custom_param("dom0_mem", parse_dom0_mem);
> > > > 
> > > > @@ -2125,7 +2123,21 @@ int construct_dom0(struct domain *d)
> > > >      BUG_ON(d->vcpu[0] == NULL);
> > > >      BUG_ON(v->is_initialised);
> > > > 
> > > > -    printk("*** LOADING DOMAIN 0 ***\n");
> > > > +    if ( dom0_mem > 0 )
> > > > +        printk("*** LOADING DOMAIN 0 ***\n");
> > > > +    else
> > > > +    {
> > > > +        int i;
> > > > +        printk("*** PLEASE SPECIFY dom0_mem PARAMETER - USING 512M FOR
> > > > NOW ***\n");
> > > > +        for (i = 0; i < 3; i++)
> > > > +        {
> > > > +            printk("%d...", i+1);
> > > > +            mdelay(1000);
> > > 
> > > There is infrastructure in Xen to print warning messages, so that we
> > > don't add delays unnecessarily.
> > > 
> > > See warning.h:warning_add.
> > 
> > I added the delay on purpose to force the user to specify dom0_mem, as
> > we cannot find a way to set a sensible default. The alternative is to
> > panic.
> 
> warning_add will gather the warning message and then will be printed at the
> end of the boot with a delay. This is what is used for sync_console message
> and also FEP on x86.
> 
> I think this is a good idea to gather all the warnings and print them at the
> end. At least it is not lost in the noise.

Yes, warning_add works very well actually. I'll use it.

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