From: Stefano Stabellini <sstabellini@kernel.org>
To: Oleksandr <olekstysh@gmail.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>, Julien Grall <julien@xen.org>
Subject: Re: [PATCH V3 4/6] xen/unpopulated-alloc: Add mechanism to use Xen resource
Date: Tue, 7 Dec 2021 15:36:53 -0800 (PST) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2112071506370.4091490@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <c2e8c00a-3856-8330-8e8f-ab8a92e93e47@gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2890 bytes --]
On Thu, 25 Nov 2021, Oleksandr wrote:
> > > Please note the following:
> > > for V3 arch_xen_unpopulated_init() was moved to init() as was agreed
> > > and gained __init specifier. So the target_resource is initialized there.
> > >
> > > With current patch series applied if CONFIG_XEN_UNPOPULATED_ALLOC
> > > is enabled:
> > >
> > > 1. On Arm, under normal circumstances, the xen_alloc_unpopulated_pages()
> > > won't be called “before” arch_xen_unpopulated_init(). It will only be
> > > called "before" when either ACPI is in use or something wrong happened
> > > with DT (and we failed to read xen_grant_frames), so we fallback to
> > > xen_xlate_map_ballooned_pages() in arm/xen/enlighten.c:xen_guest_init(),
> > > please see "arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT"
> > > for details. But in that case, I think, it doesn't matter much whether
> > > xen_alloc_unpopulated_pages() is called "before" of "after"
> > > target_resource
> > > initialization, as we don't have extended regions in place the
> > > target_resource
> > > will remain invalid even after initialization, so
> > > xen_alloc_ballooned_pages()
> > > will be used in both scenarios.
> > >
> > > 2. On x86, I am not quite sure which modes use unpopulated-alloc (PVH?),
> > > but it looks like xen_alloc_unpopulated_pages() can (and will) be called
> > > “before” arch_xen_unpopulated_init().
> > > At least, I see that xen_xlate_map_ballooned_pages() is called in
> > > x86/xen/grant-table.c:xen_pvh_gnttab_setup(). According to the initcall
> > > levels for both xen_pvh_gnttab_setup() and init() I expect the former
> > > to be called earlier.
> > > If it is true, the sentence in the commit description which mentions
> > > that “behaviour on x86 is not changed” is not precise. I don’t think
> > > it would be correct to fallback to xen_alloc_ballooned_pages() just
> > > because we haven’t initialized target_resource yet (on x86 it is just
> > > assigning it iomem_resource), at least this doesn't look like an expected
> > > behaviour and unlikely would be welcome.
> > >
> > > I am wondering whether it would be better to move
> > > arch_xen_unpopulated_init()
> > > to a dedicated init() marked with an appropriate initcall level
> > > (early_initcall?)
> > > to make sure it will always be called *before*
> > > xen_xlate_map_ballooned_pages().
> > > What do you think?
>
> ... here (#2). Or I really missed something and there wouldn't be an issue?
Yes, I see your point. Yeah, it makes sense to make sure that
drivers/xen/unpopulated-alloc.c:init is executed before
xen_pvh_gnttab_setup.
If we move it to early_initcall, then we end up running it before
xen_guest_init on ARM. But that might be fine: it looks like it should
work OK and would also allow us to execute xen_xlate_map_ballooned_pages
with target_resource already set.
So I'd say go for it :)
next prev parent reply other threads:[~2021-12-07 23:37 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-24 20:53 [PATCH V3 0/6] xen: Add support of extended regions (safe ranges) on Arm Oleksandr Tyshchenko
2021-11-24 20:53 ` [PATCH V3 1/6] xen/unpopulated-alloc: Drop check for virt_addr_valid() in fill_list() Oleksandr Tyshchenko
2021-11-24 20:53 ` [PATCH V3 2/6] arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT Oleksandr Tyshchenko
2021-11-24 23:35 ` Stefano Stabellini
2021-11-25 11:41 ` Oleksandr
2021-11-24 20:53 ` [PATCH V3 3/6] xen/balloon: Bring alloc(free)_xenballooned_pages helpers back Oleksandr Tyshchenko
2021-11-24 23:36 ` Stefano Stabellini
2021-11-24 20:53 ` [PATCH V3 4/6] xen/unpopulated-alloc: Add mechanism to use Xen resource Oleksandr Tyshchenko
2021-11-25 1:03 ` Stefano Stabellini
2021-11-25 14:01 ` Oleksandr
2021-12-07 23:36 ` Stefano Stabellini [this message]
2021-12-09 0:04 ` Oleksandr
2021-12-09 0:59 ` Stefano Stabellini
2021-11-26 15:17 ` Boris Ostrovsky
2021-11-26 15:23 ` Oleksandr
2021-11-24 20:53 ` [PATCH V3 5/6] arm/xen: Read extended regions from DT and init " Oleksandr Tyshchenko
2021-11-25 1:07 ` Stefano Stabellini
2021-11-24 20:53 ` [PATCH V3 6/6] dt-bindings: xen: Clarify "reg" purpose Oleksandr Tyshchenko
2021-11-25 1:09 ` Stefano Stabellini
2021-11-25 12:21 ` Oleksandr
2021-11-29 1:01 ` Rob Herring
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