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Re: [Xen-devel] [PATCH v2] x86/shadow: adjust minimum allocation calculations

On Thu, Feb 7, 2019 at 11:42 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
> A previously bad situation has become worse with the early setting of
> ->max_vcpus: The value returned by shadow_min_acceptable_pages() has
> further grown, and hence now holds back even more memory from use for
> the p2m.
> Make sh_min_allocation() account for all p2m memory needed for
> shadow_enable() to succeed during domain creation (at which point the
> domain has no memory at all allocated to it yet, and hence use of
> d->tot_pages is meaningless).
> Also make shadow_min_acceptable_pages() no longer needlessly add 1 to
> the vCPU count.
> Finally make the debugging printk() in shadow_alloc_p2m_page() a little
> more useful by logging some of the relevant domain settings.
> Reported-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> v2: Drop cpu_has_vmx dependency (to cover future SVM code as well).
> ---
> TBD: The question of course is whether such an "exact" calculation isn't
>      a little risky going forward, the more that the regression here
>      wasn't found by osstest, because domains with sufficiently few
>      vCPU-s weren't affected, due to the 4Mb minimum allocation enforced
>      by shadow_enable()'s call to shadow_set_allocation(). I would,
>      however, question this enforcement of a static minimum as well -
>      shadow_one_bit_enable() doesn't do so, for example.

This whole thing could use some rationalization; but this will do for
now I think:

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx.

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