From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
"Wei Liu" <wl@xen.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Ian Jackson" <ian.jackson@eu.citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>,
"Julien Grall" <julien.grall@arm.com>,
"Tamas K Lengyel" <tamas@tklengyel.com>,
xen-devel@lists.xenproject.org,
"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 16/17] xen/mm: Convert {s, g}et_gpfn_from_mfn() to use typesafe MFN
Date: Mon, 30 Mar 2020 10:10:48 +0200 [thread overview]
Message-ID: <de2c3932-9d8e-4f34-d966-4f0aaf372453@suse.com> (raw)
In-Reply-To: <c640eb5b-224f-e99a-daa2-6def00780e54@xen.org>
On 28.03.2020 12:14, Julien Grall wrote:
> On 27/03/2020 13:15, Jan Beulich wrote:
>> On 22.03.2020 17:14, julien@xen.org wrote:
>>> @@ -983,19 +984,20 @@ long p2m_pt_audit_p2m(struct p2m_domain *p2m)
>>> /* check for 1GB super page */
>>> if ( l3e_get_flags(l3e[i3]) & _PAGE_PSE )
>>> {
>>> - mfn = l3e_get_pfn(l3e[i3]);
>>> - ASSERT(mfn_valid(_mfn(mfn)));
>>> + mfn = l3e_get_mfn(l3e[i3]);
>>> + ASSERT(mfn_valid(mfn));
>>> /* we have to cover 512x512 4K pages */
>>> for ( i2 = 0;
>>> i2 < (L2_PAGETABLE_ENTRIES * L1_PAGETABLE_ENTRIES);
>>> i2++)
>>> {
>>> - m2pfn = get_gpfn_from_mfn(mfn+i2);
>>> + m2pfn = get_pfn_from_mfn(mfn_add(mfn, i2));
>>> if ( m2pfn != (gfn + i2) )
>>> {
>>> pmbad++;
>>> - P2M_PRINTK("mismatch: gfn %#lx -> mfn %#lx -> gfn %#lx\n",
>>> - gfn + i2, mfn + i2, m2pfn);
>>> + P2M_PRINTK("mismatch: gfn %#lx -> mfn %"PRI_mfn" gfn %#lx\n",
>>> + gfn + i2, mfn_x(mfn_add(mfn, i2)),
>>
>> As in the earlier patch, "mfn_x(mfn) + i2" would be shorter and
>> hence imo preferable, especially in printk() and alike invocations.
>
> The goal of using typesafe is to make the code safer not try to
> open-code everything because it might be shorter to write.
I'm not talking about "everything". As soon as you use mfn_x()
_anywhere_, type-safety is gone. Since in printk() and alike you
unavoidably have to use it (at least for now), there's no win
from using e.g. mfn_add() as you do here, imo. And hence the
readability aspect gets even higher significance.
>> I would also prefer if you left %#lx alone, with the 2nd best
>> option being to also use PRI_gfn alongside PRI_mfn. Primarily
>> I'd like to avoid having a mixture.
> The two options would be wrong:
> * gfn is an unsigned long and not gfn_t, so using PRI_gfn would be incorrect
> * mfn is now an mfn_t so using %lx would be incorrect
>
> So the format string used in the patch is correct based on the types used.
Hmm, xen/mm.h suggests a partial connection between e.g. mfn_t
and PRI_mfn, yes, but I think this is unhelpful as long as
mfn_x() needs to be explicitly used when specifying the printk()
arguments. Instead I view PRI_mfn and alike as a more general
format usable also for MFNs stored in unsigned long rather than
mfn_t.
I agree though that views here may differ. Hence wider agreement
on what the intentions are (also mid/long term), and hence how
well formed code ought to look like, would seem necessary here.
> This...
>
>>
>> Same (for both) at least one more time further down.
>
> ... would likely be applicable for all the other uses.
Agreed.
>>> --- a/xen/include/asm-x86/mm.h
>>> +++ b/xen/include/asm-x86/mm.h
>>> @@ -500,9 +500,10 @@ extern paddr_t mem_hotplug;
>>> */
>>> extern bool machine_to_phys_mapping_valid;
>>> -static inline void set_gpfn_from_mfn(unsigned long mfn, unsigned long pfn)
>>> +static inline void set_pfn_from_mfn(mfn_t mfn_, unsigned long pfn)
>>> {
>>> - const struct domain *d = page_get_owner(mfn_to_page(_mfn(mfn)));
>>> + const unsigned long mfn = mfn_x(mfn_);
>>
>> I think it would be better overall if the parameter was named
>> "mfn" and there was no local variable altogether. This would
>> bring things in line with ...
>
> You asked for this approach on the previous version [1]:
>
> "Btw, the cheaper (in terms of code churn) change here would seem to
> be to name the function parameter mfn_, and the local variable mfn.
> That'll also reduce the number of uses of the unfortunate trailing-
> underscore-name."
>
> So can you pick a side and stick with it?
Well, things like this happen when you see the final result, sorry.
And indeed I recalled commenting on this before, but upon searching
I didn't manage to find the earlier reply, to better justify what I
also suspected might have been a change of mind.
Jan
next prev parent reply other threads:[~2020-03-30 8:11 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-22 16:14 [Xen-devel] [PATCH 00/17] Bunch of typesafe conversion julien
2020-03-22 16:14 ` [Xen-devel] [PATCH 01/17] xen/x86: Introduce helpers to generate/convert the CR3 from/to a MFN/GFN julien
2020-03-25 14:46 ` Jan Beulich
2020-03-28 10:14 ` Julien Grall
2020-03-30 7:38 ` Jan Beulich
2020-04-16 11:50 ` Julien Grall
2020-03-22 16:14 ` [Xen-devel] [PATCH 02/17] xen/x86_64: Convert do_page_walk() to use typesafe MFN julien
2020-03-25 14:51 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 03/17] xen/mm: Move the MM types in a separate header julien
2020-03-25 15:00 ` Jan Beulich
2020-03-25 18:09 ` Julien Grall
2020-03-26 9:02 ` Jan Beulich
2020-03-28 10:15 ` Julien Grall
2020-03-22 16:14 ` [Xen-devel] [PATCH 04/17] xen: Convert virt_to_mfn() and mfn_to_virt() to use typesafe MFN julien
2020-03-25 15:27 ` Jan Beulich
2020-03-25 18:21 ` Julien Grall
2020-03-26 9:09 ` Jan Beulich
2020-03-28 10:33 ` Julien Grall
2020-03-22 16:14 ` [Xen-devel] [PATCH 05/17] xen/x86: Remove the non-typesafe version of pagetable_* helpers julien
2020-03-26 15:39 ` Jan Beulich
2020-03-28 10:52 ` Julien Grall
2020-03-30 7:52 ` Jan Beulich
2020-04-18 10:23 ` Julien Grall
2020-04-20 9:16 ` Jan Beulich
2020-04-20 10:10 ` Julien Grall
2020-04-20 12:14 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 06/17] xen/x86: mm: Fix the comment on top put_page_from_l2e() to use 'mfn' julien
2020-03-26 15:51 ` Jan Beulich
2020-04-18 10:54 ` Julien Grall
2020-03-22 16:14 ` [Xen-devel] [PATCH 07/17] xen/x86: traps: Convert __page_fault_type() to use typesafe MFN julien
2020-03-26 15:54 ` Jan Beulich
2020-04-18 11:01 ` Julien Grall
2020-04-18 11:43 ` Julien Grall
2020-04-20 9:19 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 08/17] xen/x86: traps: Convert show_page_walk() " julien
2020-03-22 16:14 ` [Xen-devel] [PATCH 09/17] xen/x86: Reduce the number of use of l*e_{from, get}_pfn() julien
2020-03-27 10:52 ` Jan Beulich
2020-03-28 10:53 ` Julien Grall
2020-03-22 16:14 ` [Xen-devel] [PATCH 10/17] xen/x86: pv: Use maddr_to_mfn(...) instead of the open-coding version julien
2020-03-27 11:34 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 11/17] xen/x86: nested_ept: Fix typo in the message in nept_translate_l2ga() julien
2020-03-27 11:35 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 12/17] xen/x86: p2m: Remove duplicate error message in p2m_pt_audit_p2m() julien
2020-03-27 11:35 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 13/17] xen/x86: p2m: Reflow P2M_PRINTK()s " julien
2020-03-27 11:36 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 14/17] xen/x86: mm: Re-implement set_gpfn_from_mfn() as a static inline function julien
2020-03-27 12:44 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 15/17] xen/x86: p2m: Rework printk format in audit_p2m() julien
2020-03-27 12:45 ` Jan Beulich
2020-03-22 16:14 ` [Xen-devel] [PATCH 16/17] xen/mm: Convert {s, g}et_gpfn_from_mfn() to use typesafe MFN julien
2020-03-23 12:11 ` Hongyan Xia
2020-03-23 12:26 ` Julien Grall
2020-03-27 13:15 ` Jan Beulich
2020-03-28 11:14 ` Julien Grall
2020-03-30 8:10 ` Jan Beulich [this message]
2020-03-22 16:14 ` [Xen-devel] [PATCH 17/17] xen: Switch parameter in get_page_from_gfn to use typesafe gfn julien
2020-03-23 8:37 ` Paul Durrant
2020-03-23 10:26 ` Julien Grall
2020-03-27 13:50 ` Jan Beulich
2020-03-27 13:59 ` 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=de2c3932-9d8e-4f34-d966-4f0aaf372453@suse.com \
--to=jbeulich@suse.com \
--cc=Volodymyr_Babchuk@epam.com \
--cc=andrew.cooper3@citrix.com \
--cc=george.dunlap@citrix.com \
--cc=ian.jackson@eu.citrix.com \
--cc=julien.grall@arm.com \
--cc=julien@xen.org \
--cc=roger.pau@citrix.com \
--cc=sstabellini@kernel.org \
--cc=tamas@tklengyel.com \
--cc=wl@xen.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).