xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH v3 26/28] xen/arm64: head: Use a page mapping for the 1:1 mapping in create_page_tables()
Date: Tue, 17 Sep 2019 18:53:42 +0100	[thread overview]
Message-ID: <b0633e83-cb2f-12fd-3c9e-73a6bceb9ef9@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1908231754060.26226@sstabellini-ThinkPad-T480s>

Hi Stefano,

On 8/24/19 2:16 AM, Stefano Stabellini wrote:
> On Mon, 12 Aug 2019, Julien Grall wrote:
>>           lsr   x2, x19, #THIRD_SHIFT  /* Base address for 4K mapping */
>>           lsl   x2, x2, #THIRD_SHIFT
>> @@ -674,21 +591,80 @@ create_page_tables:
>>           cmp   x1, #(LPAE_ENTRIES<<3) /* 512 entries per page */
>>           b.lt  1b
> 
> Why can't we use create_mapping_entry here?

If we re-use create_mapping_entry, then we will compute everything at 
each loop.

At the moment, the loop execute 3 instructions (excluding the branch and 
comparison). We would end up to have an extra 5 instructions for arm64 
(9 instruction for arm32).

At the moment, we iterate 512 times the loop, so this adds 2560 
instructions (resp. 4608) in the boot code. Long-term plan, we will want 
to increase the Xen mapping to 4MB (so you double up the number iteration).

This is a less than ideal solution. I haven't come up with a clever 
solution so far, hence why it is left alone.

> 
> 
>> -        /* Defer fixmap and dtb mapping until after paging enabled, to
>> -         * avoid them clashing with the 1:1 mapping. */
>> +        /*
>> +         * If Xen is loaded at exactly XEN_VIRT_START then we don't
>> +         * need an additional 1:1 mapping, the virtual mapping will
>> +         * suffice.
>> +         */
>> +        cmp   x19, #XEN_VIRT_START
>> +        bne   1f
>> +        ret
>> +1:
>> +        /*
>> +         * Only the first page of Xen will be part of the 1:1 mapping.
>> +         * All the boot_*_id tables are linked together even if they may
>> +         * not be all used. They will then be linked to the boot page
>> +         * tables at the correct level.
>> +         */
>> +        create_table_entry boot_first_id, boot_second_id, x19, FIRST_SHIFT, x0, x1, x2
>> +        create_table_entry boot_second_id, boot_third_id, x19, SECOND_SHIFT, x0, x1, x2
> 
> If I understood the code right, it is not actually required to link
> boot_first_id -> boot_second_id and/or boot_second_id -> boot_third_id:
> it depends on whether x19 clashes with XEN_FIRST_SLOT, XEN_SECOND_SLOT,
> etc. Do you think it would be possible without making the code complex
> to only call create_table_entry boot_first_id, boot_second_id and
> create_table_entry boot_second_id, boot_third_id when required?  So
> moving the calls below after the relevant checks? It looks like it could
> be done by adding those calls before "ret". I wouldn't mind if they are
> duplicated but we could avoid it by adding appropriate labels and having
> a single return path:
> 
> out1:
>    create_table_entry boot_first_id, boot_second_id, x19, FIRST_SHIFT, x0, x1, x2
> out2:
>    create_table_entry boot_second_id, boot_third_id, x19, SECOND_SHIFT, x0, x1, x2
> out3:
>    ret

I have implemented something similar. I will send it as part of the next 
version in a bit.

Cheers,

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

  reply	other threads:[~2019-09-17 17:54 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-12 17:29 [Xen-devel] [PATCH v3 00/28] xen/arm: Rework head.S to make it more compliant with the Arm Arm Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 01/28] xen/arm: lpae: Allow more LPAE helpers to be used in assembly Julien Grall
2019-08-22 17:07   ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 02/28] xen/arm64: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-08-22 17:58   ` Stefano Stabellini
2019-08-22 18:25     ` Julien Grall
2019-08-22 18:29       ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 03/28] xen/arm64: head: Rework and document setup_fixmap() Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 04/28] xen/arm64: head: Rework and document launch() Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 05/28] xen/arm64: head: Setup TTBR_EL2 in enable_mmu() and add missing isb Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 06/28] xen/arm64: head: Introduce a macro to get a PC-relative address of a symbol Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 07/28] xen/arm64: head: Fix typo in the documentation on top of init_uart() Julien Grall
2019-08-22 17:08   ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 08/28] xen/arm32: head: Add a macro to move an immediate constant into a 32-bit register Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 09/28] xen/arm32: head: Mark the end of subroutines with ENDPROC Julien Grall
2019-08-12 17:33   ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 10/28] xen/arm32: head: Don't clobber r14/lr in the macro PRINT Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 11/28] xen/arm32: head: Rework UART initialization on boot CPU Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 12/28] xen/arm32: head: Introduce print_reg Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 13/28] xen/arm32: head: Introduce distinct paths for the boot CPU and secondary CPUs Julien Grall
2019-08-22 17:11   ` Stefano Stabellini
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 14/28] xen/arm32: head: Rework and document check_cpu_mode() Julien Grall
2019-08-22 17:14   ` Stefano Stabellini
2019-09-07 10:35     ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 15/28] xen/arm32: head: Rework and document zero_bss() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 16/28] xen/arm32: head: Document create_pages_tables() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 17/28] xen/arm32: head: Document enable_mmu() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 18/28] xen/arm32: head: Move assembly switch to the runtime PT in secondary CPUs path Julien Grall
2019-08-22 17:17   ` Stefano Stabellini
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 19/28] xen/arm32: head: Don't setup the fixmap on secondary CPUs Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 20/28] xen/arm32: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-08-22 18:17   ` Stefano Stabellini
2019-08-22 18:31     ` Julien Grall
2019-08-22 22:53       ` Stefano Stabellini
2019-08-22 23:39         ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 21/28] xen/arm32: head: Rework and document setup_fixmap() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 22/28] xen/arm32: head: Rework and document launch() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 23/28] xen/arm32: head: Setup HTTBR in enable_mmu() and add missing isb Julien Grall
2019-08-22 17:15   ` Stefano Stabellini
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 24/28] xen/arm: Zero BSS after the MMU and D-cache is turned on Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 25/28] xen/arm64: head: Introduce macros to create table and mapping entry Julien Grall
2019-08-22 23:31   ` Stefano Stabellini
2019-08-22 23:44     ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 26/28] xen/arm64: head: Use a page mapping for the 1:1 mapping in create_page_tables() Julien Grall
2019-08-24  1:16   ` Stefano Stabellini
2019-09-17 17:53     ` Julien Grall [this message]
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 27/28] xen/arm32: head: Introduce macros to create table and mapping entry Julien Grall
2019-08-23  1:10   ` Stefano Stabellini
2019-08-23  9:40     ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 28/28] xen/arm32: head: Use a page mapping for the 1:1 mapping in create_page_tables() Julien Grall

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=b0633e83-cb2f-12fd-3c9e-73a6bceb9ef9@arm.com \
    --to=julien.grall@arm.com \
    --cc=Volodymyr_Babchuk@epam.com \
    --cc=sstabellini@kernel.org \
    --cc=xen-devel@lists.xenproject.org \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
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).