Re: [Xen-devel] [PATCH for-4.12 4/8] x86/shadow: alloc enough pages so initialization doesn't fail

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Feb 05, 2019 at 10:32:08AM -0700, Jan Beulich wrote:
> >>> On 05.02.19 at 16:53, <roger.pau@xxxxxxxxxx> wrote:
> > On Tue, Feb 05, 2019 at 08:15:27AM -0700, Jan Beulich wrote:
> >> >>> On 05.02.19 at 14:52, <roger.pau@xxxxxxxxxx> wrote:
> >> > I don't think the amount of guest memory matters here, the following
> >> > example with 8G of RAM and 8 vCPUs fails in the same way:
> >> > 
> >> > # cat test.c
> >> > test.c       test.c.gcov  test.cfg     test.core
> >> > root@:~ # cat test.cfg
> >> > name = "test"
> >> > type = "hvm"
> >> > 
> >> > memory = 8192
> >> > vcpus = 8
> >> > hap = 0
> >> > # xl create test.cfg
> >> > Parsing config from test.cfg
> >> > libxl: error: libxl_create.c:578:libxl__domain_make: domain creation 
> >> > fail: 
> >> > Cannot allocate memory
> >> > libxl: error: libxl_create.c:975:initiate_domain_create: cannot make 
> >> > domain: 
> >> > -3
> >> > 
> >> > And I think that's a perfectly suitable guest config.
> >> 
> >> Indeed. And it doesn't seem to work for me anymore either. Must be
> >> a regression, as I'm pretty sure it did still work not all that long ago.
> >> Not even "shadow_memory=256" helps.
> > 
> > No, because shadow_init is called from domain_create, and it's
> > impossible to increase the shadow memory pool before the domain is
> > actually created.
> 
> Okay, I misunderstood the problem initially. Aiui this is a
> regression from the early setting of ->max_vcpus, as that now

Ahh, I wasn't able to figure out what caused this regression, it's
indeed caused by max_vcpus being set at domain_create.

> causes shadow_min_acceptable_pages() to block far more pages
> than it did before from use for p2m allocs during domain creation.
> I think I see an alternative way of fixing this for the moment
> (without adding re-size logic yet when d->tot_pages grows), but
> this will have to wait until tomorrow.

Ack, I'm happy to implement it if you tell me the plan :).

Maybe as an alternative the checks in shadow_alloc_p2m_page can be
relaxed during domain creation, or the p2m allocated when the first
memory page gets added to the domain?

Thanks, Roger.

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