LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
To: dri-devel@lists.freedesktop.org
Cc: Rob Herring <robh@kernel.org>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	Steven Price <steven.price@arm.com>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	linux-kernel@vger.kernel.org,
	Chris Morgan <macromorgan@hotmail.com>,
	stable@vger.kernel.org
Subject: [PATCH 1/3] drm/panfrost: Simplify lock_region calculation
Date: Fri, 20 Aug 2021 17:31:15 -0400	[thread overview]
Message-ID: <20210820213117.13050-2-alyssa.rosenzweig@collabora.com> (raw)
In-Reply-To: <20210820213117.13050-1-alyssa.rosenzweig@collabora.com>

In lock_region, simplify the calculation of the region_width parameter.
This field is the size, but encoded as log2(ceil(size)) - 1.
log2(ceil(size)) may be computed directly as fls(size - 1). However, we
want to use the 64-bit versions as the amount to lock can exceed
32-bits.

This avoids undefined behaviour when locking all memory (size ~0),
caught by UBSAN.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reported-and-tested-by: Chris Morgan <macromorgan@hotmail.com>
Cc: <stable@vger.kernel.org>
---
 drivers/gpu/drm/panfrost/panfrost_mmu.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 0da5b3100ab1..f6e02d0392f4 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -62,21 +62,12 @@ static void lock_region(struct panfrost_device *pfdev, u32 as_nr,
 {
 	u8 region_width;
 	u64 region = iova & PAGE_MASK;
-	/*
-	 * fls returns:
-	 * 1 .. 32
-	 *
-	 * 10 + fls(num_pages)
-	 * results in the range (11 .. 42)
-	 */
-
-	size = round_up(size, PAGE_SIZE);
 
-	region_width = 10 + fls(size >> PAGE_SHIFT);
-	if ((size >> PAGE_SHIFT) != (1ul << (region_width - 11))) {
-		/* not pow2, so must go up to the next pow2 */
-		region_width += 1;
-	}
+	/* The size is encoded as ceil(log2) minus(1), which may be calculated
+	 * with fls. The size must be clamped to hardware bounds.
+	 */
+	size = max_t(u64, size, PAGE_SIZE);
+	region_width = fls64(size - 1) - 1;
 	region |= region_width;
 
 	/* Lock the region that needs to be updated */
-- 
2.30.2


  reply	other threads:[~2021-08-20 21:31 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20 21:31 [PATCH 0/3] drm/panfrost: Bug fixes for lock_region Alyssa Rosenzweig
2021-08-20 21:31 ` Alyssa Rosenzweig [this message]
2021-08-23  9:40   ` [PATCH 1/3] drm/panfrost: Simplify lock_region calculation Steven Price
2021-08-23 21:09     ` Alyssa Rosenzweig
2021-08-23 21:54       ` Steven Price
2021-08-20 21:31 ` [PATCH 2/3] drm/panfrost: Use u64 for size in lock_region Alyssa Rosenzweig
2021-08-23  9:40   ` Steven Price
2021-08-23 21:11     ` Alyssa Rosenzweig
2021-08-23 21:57       ` Steven Price
2021-08-20 21:31 ` [PATCH 3/3] drm/panfrost: Clamp lock region to Bifrost minimum Alyssa Rosenzweig
2021-08-23  9:40   ` Steven Price
2021-08-23 21:13     ` Alyssa Rosenzweig
2021-08-23 22:02       ` Steven Price

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=20210820213117.13050-2-alyssa.rosenzweig@collabora.com \
    --to=alyssa.rosenzweig@collabora.com \
    --cc=airlied@linux.ie \
    --cc=daniel@ffwll.ch \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=macromorgan@hotmail.com \
    --cc=robh@kernel.org \
    --cc=stable@vger.kernel.org \
    --cc=steven.price@arm.com \
    --cc=tomeu.vizoso@collabora.com \
    --subject='Re: [PATCH 1/3] drm/panfrost: Simplify lock_region calculation' \
    /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).