xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	 xen-devel@lists.xenproject.org, Wei.Chen@arm.com,
	Henry.Wang@arm.com,  Penny.Zheng@arm.com,
	Bertrand.Marquis@arm.com,  Julien Grall <jgrall@amazon.com>,
	 Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH RFCv2 10/15] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap
Date: Mon, 17 May 2021 17:37:25 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.21.2105171736450.14426@sstabellini-ThinkPad-T480s> (raw)
In-Reply-To: <602bea61-9db2-a27d-1fed-001e2b5b2176@xen.org>

On Sat, 15 May 2021, Julien Grall wrote:
> Hi Stefano,
> 
> On 13/05/2021 23:27, Stefano Stabellini wrote:
> > On Thu, 13 May 2021, Julien Grall wrote:
> > > Hi Stefano,
> > > 
> > > On 12/05/2021 23:44, Stefano Stabellini wrote:
> > > > On Sun, 25 Apr 2021, Julien Grall wrote:
> > > > > From: Julien Grall <jgrall@amazon.com>
> > > > > 
> > > > > xen_{un,}map_table() already uses the helper to map/unmap pages
> > > > > on-demand (note this is currently a NOP on arm64). So switching to
> > > > > domheap don't have any disavantage.
> > > > > 
> > > > > But this as the benefit:
> > > > >       - to keep the page tables unmapped if an arch decided to do so
> > > > >       - reduce xenheap use on arm32 which can be pretty small
> > > > > 
> > > > > Signed-off-by: Julien Grall <jgrall@amazon.com>
> > > > 
> > > > Thanks for the patch. It looks OK but let me ask a couple of questions
> > > > to clarify my doubts.
> > > > 
> > > > This change should have no impact to arm64, right?
> > > > 
> > > > For arm32, I wonder why we were using map_domain_page before in
> > > > xen_map_table: it wasn't necessary, was it? In fact, one could even say
> > > > that it was wrong?
> > > In xen_map_table() we need to be able to map pages from Xen binary,
> > > xenheap...
> > > On arm64, we would be able to use mfn_to_virt() because everything is
> > > mapped
> > > in Xen. But that's not the case on arm32. So we need a way to map anything
> > > easily.
> > > 
> > > The only difference between xenheap and domheap are the former is always
> > > mapped while the latter may not be. So one can also view a xenheap page as
> > > a
> > > glorified domheap.
> > > 
> > > I also don't really want to create yet another interface to map pages (we
> > > have
> > > vmap(), map_domain_page(), map_domain_global_page()...). So, when I
> > > implemented xen_map_table() a couple of years ago, I came to the
> > > conclusion
> > > that this is a convenient (ab)use of the interface.
> > 
> > Got it. Repeating to check if I see the full picture. On ARM64 there are
> > no changes. On ARM32, at runtime there are no changes mapping/unmapping
> > pages because xen_map_table is already mapping all pages using domheap,
> > even xenheap pages are mapped as domheap; so this patch makes no
> > difference in mapping/unmapping, correct?
> 
> For arm32, it makes a slight difference when allocating a new page table (we
> didn't call map/unmap before) but this is not called often.
> 
> The main "drop" in performance happened when xen_{,map}_table() was
> introduced.
> 
> > 
> > The only difference is that on arm32 we are using domheap to allocate
> > the pages, which is a different (larger) pool.
> 
> Yes.
> 
> Would you be happy to give you acked-by/reviewed-by on this basis?

Yes

Acked-by: Stefano Stabellini <sstabellini@kernel.org>


  reply	other threads:[~2021-05-18  0:37 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-25 20:13 [PATCH RFCv2 00/15] xen/arm: mm: Remove open-coding mappings Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 01/15] xen/arm: lpae: Rename LPAE_ENTRIES_MASK_GS to LPAE_ENTRY_MASK_GS Julien Grall
2021-05-11 22:12   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 02/15] xen/arm: lpae: Use the generic helpers to defined the Xen PT helpers Julien Grall
2021-05-11 22:26   ` Stefano Stabellini
2021-05-12 14:26     ` Julien Grall
2021-05-12 21:30       ` Stefano Stabellini
2021-05-12 22:16         ` Julien Grall
2021-05-13 22:44           ` Stefano Stabellini
2021-07-03 17:32             ` Julien Grall
2021-07-13 20:53               ` Stefano Stabellini
2021-07-14 17:40                 ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 03/15] xen/arm: p2m: Replace level_{orders, masks} arrays with LEVEL_{ORDER, MASK} Julien Grall
2021-05-11 22:33   ` Stefano Stabellini
2021-05-12 14:39     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 04/15] xen/arm: mm: Allow other mapping size in xen_pt_update_entry() Julien Grall
2021-05-11 22:42   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 05/15] xen/arm: mm: Avoid flushing the TLBs when mapping are inserted Julien Grall
2021-05-11 22:51   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 06/15] xen/arm: mm: Don't open-code Xen PT update in remove_early_mappings() Julien Grall
2021-05-11 22:58   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 07/15] xen/arm: mm: Re-implement early_fdt_map() using map_pages_to_xen() Julien Grall
2021-05-12 21:41   ` Stefano Stabellini
2021-05-12 22:18     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 08/15] xen/arm32: mm: Check if the virtual address is shared before updating it Julien Grall
2021-05-12 22:00   ` Stefano Stabellini
2021-05-12 22:23     ` Julien Grall
2021-05-13 22:32       ` Stefano Stabellini
2021-05-13 22:59         ` Julien Grall
2021-05-14  1:04           ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 09/15] xen/arm32: mm: Re-implement setup_xenheap_mappings() using map_pages_to_xen() Julien Grall
2021-05-12 22:07   ` Stefano Stabellini
2021-05-13 17:55     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 10/15] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap Julien Grall
2021-05-12 22:44   ` Stefano Stabellini
2021-05-13 18:09     ` Julien Grall
2021-05-13 22:27       ` Stefano Stabellini
2021-05-15  8:48         ` Julien Grall
2021-05-18  0:37           ` Stefano Stabellini [this message]
2021-04-25 20:13 ` [PATCH RFCv2 11/15] xen/arm: mm: Allow page-table allocation from the boot allocator Julien Grall
2021-05-13 22:58   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 12/15] xen/arm: add Persistent Map (PMAP) infrastructure Julien Grall
2021-04-26  9:41   ` Xia, Hongyan
2021-07-03 17:57     ` Julien Grall
2021-04-28 21:47   ` Wei Liu
2021-05-14 23:25   ` Stefano Stabellini
2021-05-15  8:54     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 13/15] xen/arm: mm: Use the PMAP helpers in xen_{,un}map_table() Julien Grall
2021-05-14 23:35   ` Stefano Stabellini
2021-05-15  9:03     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 14/15] xen/arm: mm: Rework setup_xenheap_mappings() Julien Grall
2021-05-14 23:51   ` Stefano Stabellini
2021-05-15  9:21     ` Julien Grall
2021-05-18  0:50       ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 15/15] xen/arm: mm: Re-implement setup_frame_table_mappings() with map_pages_to_xen() Julien Grall
2021-05-15  0:02   ` Stefano Stabellini
2021-05-15  9:25     ` Julien Grall
2021-05-18  0:51       ` Stefano Stabellini

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=alpine.DEB.2.21.2105171736450.14426@sstabellini-ThinkPad-T480s \
    --to=sstabellini@kernel.org \
    --cc=Bertrand.Marquis@arm.com \
    --cc=Henry.Wang@arm.com \
    --cc=Penny.Zheng@arm.com \
    --cc=Volodymyr_Babchuk@epam.com \
    --cc=Wei.Chen@arm.com \
    --cc=jgrall@amazon.com \
    --cc=julien@xen.org \
    --cc=xen-devel@lists.xenproject.org \
    --subject='Re: [PATCH RFCv2 10/15] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).