On 20/08/2021 22:31, Alyssa Rosenzweig wrote:

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.

It might have been useful to mention what it is that UBSAN specifically picked up (it took me a while to spot) - but anyway I think there's a bigger issue with it being completely wrong when size == ~0 (see below).

Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Reported-and-tested-by: Chris Morgan macromorgan@hotmail.com Cc: stable@vger.kernel.org

However, I've confirmed this returns the same values and is certainly more simple, so:

Reviewed-by: Steven Price steven.price@arm.com

---

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);

This seems to be the first issue - ~0 will be 'rounded up' to 0.

• region_width = 10 + fls(size >> PAGE_SHIFT);

fls(0) == 0, so region_width == 10.

• if ((size >> PAGE_SHIFT) != (1ul << (region_width - 11))) {

Presumably here's where UBSAN objects - we're shifting by a negative value, which even it it happens to works means the lock region is tiny and certainly not what was intended! It might well be worth a:

Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")

Note for anyone following along at (working-from-) home: although this code was cargo culted from kbase - kbase is fine because it takes a pfn and doesn't do the round_up() stage.

Which also exposes the second bug (fixed in patch 2): a size_t isn't big enough on 32 bit platforms (all Midgard/Bifrost GPUs have a VA size bigger than 32 bits). Again kbase gets away with a u32 because it's a pfn.

There is potentially a third bug which kbase only recently attempted to fix. The lock address is effectively rounded down by the hardware (the bottom bits are ignored). So if you have mask=(1<<region_width)-1 but (iova & mask) != ((iova + size) & mask) then you are potentially failing to lock the end of the intended region. kbase has added some code to handle this:

/* Round up if some memory pages spill into the next region. */ region_frame_number_start = pfn >> (lockaddr_size_log2 - PAGE_SHIFT); region_frame_number_end = (pfn + num_pages - 1) >> (lockaddr_size_log2 - PAGE_SHIFT);

if (region_frame_number_start < region_frame_number_end) lockaddr_size_log2 += 1;

I guess we should too?

Steve

• /* 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 */

On 20/08/2021 22:31, Alyssa Rosenzweig wrote:

Mali virtual addresses are 48-bit. Use a u64 instead of size_t to ensure we can express the "lock everything" condition as ~0ULL without relying on platform-specific behaviour.

'platform-specific behaviour' makes it sound like this is something to do with a particular board. This is 32bit/64bit - it's going to be broken on 32bit: large lock regions are not going to work.

Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Suggested-by: Rob Herring robh@kernel.org Tested-by: Chris Morgan macromorgan@hotmail.com

Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")

Reviewed-by: Steven Price steven.price@arm.com

Steve

---

drivers/gpu/drm/panfrost/panfrost_mmu.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index f6e02d0392f4..3a795273e505 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c @@ -58,7 +58,7 @@ static int write_cmd(struct panfrost_device *pfdev, u32 as_nr, u32 cmd) }

static void lock_region(struct panfrost_device *pfdev, u32 as_nr,

• 	u64 iova, size_t size)
  

• 	u64 iova, u64 size)
  

{ u8 region_width; u64 region = iova & PAGE_MASK; @@ -78,7 +78,7 @@ static void lock_region(struct panfrost_device *pfdev, u32 as_nr,

static int mmu_hw_do_operation_locked(struct panfrost_device *pfdev, int as_nr,

• 		      u64 iova, size_t size, u32 op)
  

• 		      u64 iova, u64 size, u32 op)
  

{ if (as_nr < 0) return 0; @@ -95,7 +95,7 @@ static int mmu_hw_do_operation_locked(struct panfrost_device *pfdev, int as_nr,

static int mmu_hw_do_operation(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,

• 	       u64 iova, size_t size, u32 op)
  

• 	       u64 iova, u64 size, u32 op)
  

{ int ret;

@@ -112,7 +112,7 @@ static void panfrost_mmu_enable(struct panfrost_device *pfdev, struct panfrost_m u64 transtab = cfg->arm_mali_lpae_cfg.transtab; u64 memattr = cfg->arm_mali_lpae_cfg.memattr;

• mmu_hw_do_operation_locked(pfdev, as_nr, 0, ~0UL, AS_COMMAND_FLUSH_MEM);

• mmu_hw_do_operation_locked(pfdev, as_nr, 0, ~0ULL, AS_COMMAND_FLUSH_MEM);

  mmu_write(pfdev, AS_TRANSTAB_LO(as_nr), transtab & 0xffffffffUL); mmu_write(pfdev, AS_TRANSTAB_HI(as_nr), transtab >> 32);

@@ -128,7 +128,7 @@ static void panfrost_mmu_enable(struct panfrost_device *pfdev, struct panfrost_m

static void panfrost_mmu_disable(struct panfrost_device *pfdev, u32 as_nr) {

• mmu_hw_do_operation_locked(pfdev, as_nr, 0, ~0UL, AS_COMMAND_FLUSH_MEM);

• mmu_hw_do_operation_locked(pfdev, as_nr, 0, ~0ULL, AS_COMMAND_FLUSH_MEM);

  mmu_write(pfdev, AS_TRANSTAB_LO(as_nr), 0); mmu_write(pfdev, AS_TRANSTAB_HI(as_nr), 0);

@@ -242,7 +242,7 @@ static size_t get_pgsize(u64 addr, size_t size)

static void panfrost_mmu_flush_range(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,

• 		     u64 iova, size_t size)
  

• 		     u64 iova, u64 size)
  

{ if (mmu->as < 0) return;

On 20/08/2021 22:31, Alyssa Rosenzweig wrote:

When locking a region, we currently clamp to a PAGE_SIZE as the minimum lock region. While this is valid for Midgard, it is invalid for Bifrost,

While the spec does seem to state it's invalid for Bifrost - kbase didn't bother with a lower clamp for a long time. I actually think this is in many ways more of a spec bug: i.e. implementation details of the round-up that the hardware does. But it's much safer following the spec ;) And it seems like kbase eventually caught up too.

where the minimum locking size is 8x larger than the 4k page size. Add a hardware definition for the minimum lock region size (corresponding to KBASE_LOCK_REGION_MIN_SIZE_LOG2 in kbase) and respect it.

Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Tested-by: Chris Morgan macromorgan@hotmail.com Cc: stable@vger.kernel.org

Reviewed-by: Steven Price steven.price@arm.com

---

drivers/gpu/drm/panfrost/panfrost_mmu.c | 2 +- drivers/gpu/drm/panfrost/panfrost_regs.h | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index 3a795273e505..dfe5f1d29763 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c @@ -66,7 +66,7 @@ static void lock_region(struct panfrost_device *pfdev, u32 as_nr, /* 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);

• size = max_t(u64, size, AS_LOCK_REGION_MIN_SIZE); region_width = fls64(size - 1) - 1; region |= region_width;

diff --git a/drivers/gpu/drm/panfrost/panfrost_regs.h b/drivers/gpu/drm/panfrost/panfrost_regs.h index 1940ff86e49a..6c5a11ef1ee8 100644 --- a/drivers/gpu/drm/panfrost/panfrost_regs.h +++ b/drivers/gpu/drm/panfrost/panfrost_regs.h @@ -316,6 +316,8 @@ #define AS_FAULTSTATUS_ACCESS_TYPE_READ (0x2 << 8) #define AS_FAULTSTATUS_ACCESS_TYPE_WRITE (0x3 << 8)

+#define AS_LOCK_REGION_MIN_SIZE (1ULL << 15)

#define gpu_write(dev, reg, data) writel(data, dev->iomem + reg) #define gpu_read(dev, reg) readl(dev->iomem + reg)