| Message ID | 20210824173028.7528-1-alyssa.rosenzweig@collabora.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | drm/panfrost: Bug fixes for lock_region | expand |
On Tue, Aug 24, 2021 at 12:30 PM Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com> wrote: > > Chris Morgan reported UBSAN errors in panfrost and tracked them down to > the size computation in lock_region. This calculation is overcomplicated > (cargo culted from kbase) and can be simplified with kernel helpers and > some mathematical identities. The first patch in the series rewrites the > calculation in a form avoiding undefined behaviour; Chris confirms it > placates UBSAN. > > While researching this function, I noticed a pair of other potential > bugs: Bifrost can lock more than 4GiB at a time, but must lock at least > 32KiB at a time. The latter patches in the series handle these cases. > > In review of v1 of this series, Steven pointed out a fourth potential > bug: rounding down the iova can truncate the lock region. v2 adds a new > patch for this case. > > The size computation was unit-tested in userspace. Relevant code below, > just missing some copypaste definitions for fls64/clamp/etc: > > #define MIN_LOCK (1ULL << 12) > #define MAX_LOCK (1ULL << 48) > > struct { > uint64_t size; > uint8_t encoded; > } tests[] = { > /* Clamping */ > { 0, 11 }, > { 1, 11 }, > { 2, 11 }, > { 4095, 11 }, > /* Power of two */ > { 4096, 11 }, > /* Round up */ > { 4097, 12 }, > { 8192, 12 }, > { 16384, 13 }, > { 16385, 14 }, > /* Maximum */ > { ~0ULL, 47 }, > }; > > static uint8_t region_width(uint64_t size) > { > size = clamp(size, MIN_LOCK, MAX_LOCK); > return fls64(size - 1) - 1; > } > > int main(int argc, char **argv) > { > for (unsigned i = 0; i < ARRAY_SIZE(tests); ++i) { > uint64_t test = tests[i].size; > uint8_t expected = tests[i].encoded; > uint8_t actual = region_width(test); > > assert(expected == actual); > } > } > > Changes in v2: > > * New patch for non-aligned lock addresses > * Commit message improvements. > * Add Steven's tags. > > Alyssa Rosenzweig (4): > drm/panfrost: Simplify lock_region calculation > drm/panfrost: Use u64 for size in lock_region > drm/panfrost: Clamp lock region to Bifrost minimum > drm/panfrost: Handle non-aligned lock addresses > > drivers/gpu/drm/panfrost/panfrost_mmu.c | 32 ++++++++++-------------- > drivers/gpu/drm/panfrost/panfrost_regs.h | 2 ++ > 2 files changed, 15 insertions(+), 19 deletions(-) For the series, Reviewed-by: Rob Herring <robh@kernel.org>
Chris Morgan reported UBSAN errors in panfrost and tracked them down to the size computation in lock_region. This calculation is overcomplicated (cargo culted from kbase) and can be simplified with kernel helpers and some mathematical identities. The first patch in the series rewrites the calculation in a form avoiding undefined behaviour; Chris confirms it placates UBSAN. While researching this function, I noticed a pair of other potential bugs: Bifrost can lock more than 4GiB at a time, but must lock at least 32KiB at a time. The latter patches in the series handle these cases. In review of v1 of this series, Steven pointed out a fourth potential bug: rounding down the iova can truncate the lock region. v2 adds a new patch for this case. The size computation was unit-tested in userspace. Relevant code below, just missing some copypaste definitions for fls64/clamp/etc: #define MIN_LOCK (1ULL << 12) #define MAX_LOCK (1ULL << 48) struct { uint64_t size; uint8_t encoded; } tests[] = { /* Clamping */ { 0, 11 }, { 1, 11 }, { 2, 11 }, { 4095, 11 }, /* Power of two */ { 4096, 11 }, /* Round up */ { 4097, 12 }, { 8192, 12 }, { 16384, 13 }, { 16385, 14 }, /* Maximum */ { ~0ULL, 47 }, }; static uint8_t region_width(uint64_t size) { size = clamp(size, MIN_LOCK, MAX_LOCK); return fls64(size - 1) - 1; } int main(int argc, char **argv) { for (unsigned i = 0; i < ARRAY_SIZE(tests); ++i) { uint64_t test = tests[i].size; uint8_t expected = tests[i].encoded; uint8_t actual = region_width(test); assert(expected == actual); } } Changes in v2: * New patch for non-aligned lock addresses * Commit message improvements. * Add Steven's tags. Alyssa Rosenzweig (4): drm/panfrost: Simplify lock_region calculation drm/panfrost: Use u64 for size in lock_region drm/panfrost: Clamp lock region to Bifrost minimum drm/panfrost: Handle non-aligned lock addresses drivers/gpu/drm/panfrost/panfrost_mmu.c | 32 ++++++++++-------------- drivers/gpu/drm/panfrost/panfrost_regs.h | 2 ++ 2 files changed, 15 insertions(+), 19 deletions(-)