Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce PGC_state_uninitialised

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Mon, 2020-03-23 at 08:49 +0000, Paul Durrant wrote:
> Ok, so deferring the call to free_heap_pages() (and consequently
> init_heap_pages()) is safe to defer until the guest is torn down? (Or
> is this only safe if the page is being assigned to the initial
> domain?)

It's intended to be safe in all cases, including pages which are
allocated from the boot allocator to be used as page tables (cf. the
early-vmap patches), etc.

We kind of have to assume that it's safe to use the page for whatever
purpose it was allocated for, for the lifetime of that usage. If *that*
isn't true, we have bigger problems.

The PGC_state_uninitialised thing is only about recycling it into the
heap *later*, once the lifetime of that initial usage has ended.

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