| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20251016092208.2b8ae536@fedora>
Date: Thu, 16 Oct 2025 09:22:08 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Loïc Molinari <loic.molinari@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
<mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
<airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Jani Nikula
<jani.nikula@...ux.intel.com>, Joonas Lahtinen
<joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
Tvrtko Ursulin <tursulin@...ulin.net>, Rob Herring <robh@...nel.org>,
Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
Melissa Wen <mwen@...lia.com>, Maíra Canal
<mcanal@...lia.com>, Hugh Dickins <hughd@...gle.com>, Baolin Wang
<baolin.wang@...ux.alibaba.com>, Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>, Mikołaj Wasiak
<mikolaj.wasiak@...el.com>, Christian Brauner <brauner@...nel.org>, Nitin
Gote <nitin.r.gote@...el.com>, Andi Shyti <andi.shyti@...ux.intel.com>,
Jonathan Corbet <corbet@....net>, Christopher Healy <healych@...zon.com>,
Matthew Wilcox <willy@...radead.org>, Bagas Sanjaya <bagasdotme@...il.com>,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
linux-doc@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v4 08/13] drm/v3d: Fix builds with
CONFIG_TRANSPARENT_HUGEPAGE=n
On Thu, 16 Oct 2025 09:09:26 +0200
Loïc Molinari <loic.molinari@...labora.com> wrote:
> Hi Boris,
>
> On 16/10/2025 07:56, Boris Brezillon wrote:
> > On Wed, 15 Oct 2025 22:41:59 +0200
> > Loïc Molinari <loic.molinari@...labora.com> wrote:
> >
> >> On 15/10/2025 20:17, Boris Brezillon wrote:
> >>> On Wed, 15 Oct 2025 17:30:12 +0200
> >>> Loïc Molinari <loic.molinari@...labora.com> wrote:
> >>>
> >>>> Don't declare "super_pages" on builds with CONFIG_TRANSPARENT_HUGEPAGE
> >>>> disabled to prevent build error:
> >>>>
> >>>> ERROR: modpost: "super_pages" [drivers/gpu/drm/v3d/v3d.ko] undefined!
> >>>
> >>> I believe this is a bug introduced by the previous commit: the
> >>> compiler probably drops any code between the
> >>> IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) check and the err label
> >>> because IS_ENABLED() evaluates to false at compile time. So I'd squash
> >>> those changes in the previous commit.
> >>
> >> Right, it's been introduced in previous commit.
> >>
> >>>
> >>>>
> >>>> Signed-off-by: Loïc Molinari <loic.molinari@...labora.com>
> >>>> ---
> >>>> drivers/gpu/drm/v3d/v3d_drv.h | 2 ++
> >>>> drivers/gpu/drm/v3d/v3d_gem.c | 2 ++
> >>>> 2 files changed, 4 insertions(+)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
> >>>> index 99a39329bb85..481502104391 100644
> >>>> --- a/drivers/gpu/drm/v3d/v3d_drv.h
> >>>> +++ b/drivers/gpu/drm/v3d/v3d_drv.h
> >>>> @@ -564,7 +564,9 @@ extern const struct dma_fence_ops v3d_fence_ops;
> >>>> struct dma_fence *v3d_fence_create(struct v3d_dev *v3d, enum v3d_queue q);
> >>>>
> >>>> /* v3d_gem.c */
> >>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >>>> extern bool super_pages;
> >>>> +#endif
> >>>> int v3d_gem_init(struct drm_device *dev);
> >>>> void v3d_gem_destroy(struct drm_device *dev);
> >>>> void v3d_reset_sms(struct v3d_dev *v3d);
> >>>> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> >>>> index 635ff0fabe7e..0039063eb8b2 100644
> >>>> --- a/drivers/gpu/drm/v3d/v3d_gem.c
> >>>> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> >>>> @@ -269,7 +269,9 @@ v3d_huge_mnt_init(struct v3d_dev *v3d)
> >>>> * match our usecase.
> >>>> */
> >>>>
> >>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >>>> if (super_pages)
> >>>> +#endif
> >>>> err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> >>>
> >>> Why not
> >>>
> >>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >>> if (super_pages)
> >>> err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> >>> #endif
> >>>
> >>> I guess
> >>>
> >>> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
> >>> err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> >>>
> >>> would also do, since it's likely to rely on the same optimization the
> >>> previous v3d_gemfs_init() implementation was relying on, but it's
> >>> fragile (not sure what happens when compiled with -O0).
> >>
> >> I'll remove the #ifdef/#endif around the super_pages declaration in
> >> v3d_drv.h because it isn't necessary if super_pages is compiled out in
> >> v3d_huge_mnt_init().
> >>
> >> In v3d_huge_mnt_init(), I'd add the #ifdef before the ret variable
> >> declaration and the #endif right after the last else so that it's clear
> >> drm_notice("THP is recommended...") is called unconditionally when
> >> CONFIG_TRANSPARENT_HUGEPAGE=n, whatever the optim level. What do you think?
> >
> > First off, I'm not a huge fan of the following pattern
> >
> > #if foo
> > if (xxxx)
> > #endif
> > do_something
> >
> > which also applies to
> >
> > #if foo
> > if (xxxx)
> > do_xxx
> > else if (yyy)
> > do_yyy
> > else
> > #endif
> > do_something
> >
> > I'd rather have do_something duplicated in an #else section
> > like that:
> >
> > #if foo
> > if (xxxx)
> > do_xxx
> > else if (yyy)
> > do_yyy
> > else
> > do_something
> > #else
> > do_something
> > #endif
> >
> > But I'm not even seeing what the problem is here. If you do:
> >
> > int err = 0;
> >
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > if (super_pages)
> > err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> > #endif
> >
> > if (v3d->drm.huge_mnt)
> > drm_info(&v3d->drm, "Using Transparent Hugepages\n");
> > else if (err)
> > drm_warn(&v3d->drm, "Can't use Transparent Hugepages (%d)\n", err);
> > else
> > drm_notice(&v3d->drm,
> > "Transparent Hugepage support is recommended for optimal performance on this platform!\n");
> >
> > You're guaranteed that err=0 and v3d->drm.huge_mnt=NULL when
> > CONFIG_TRANSPARENT_HUGEPAGE=n, so the "THP recommended"
> > message should be displayed unconditionally. Am I missing
> > something?
>
> It doesn't really matter here but I just thought it would be cleaner to
> explicitly let just the drm_notice() because the compiler doesn't know
> v3d->drm.huge_mnt is always NULL here and would emit a branch in
> CONFIG_TRANSPARENT_HUGEPAGE=n builds.
Okay, well. I think it would matter if this was a hot-path, maybe? But
that's clearly not the case, this code is called once at probe time.
> I know your dislike for this
> pattern now, so I will stick to the suggestion :)
Actually, I would probably stick to the original
if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
pattern since it worked so far. If -O0 is really a problem (didn't
check if it is), and v3d maintainers care about it (I doubt anyone
forces -O0 to be honest), they'll fix that in a follow-up patchset.
Powered by blists - more mailing lists