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CUDA: fix alignment check for FA#19023

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JohannesGaessler:cuda-fa-fix-align-check
Jan 22, 2026
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CUDA: fix alignment check for FA#19023
JohannesGaessler merged 1 commit into
ggml-org:masterfrom
JohannesGaessler:cuda-fa-fix-align-check

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@JohannesGaessler JohannesGaessler commented Jan 22, 2026

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See #18953 (comment) .

The problem has to do with the check for memory alignment. The point of the check is to avoid misaligned memory accesses which would result in a crash. But only for floating-point data is it correct to assume alignment in the first place so the check should also only be done for that data.

@JohannesGaessler JohannesGaessler mentioned this pull request Jan 22, 2026
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ggerganov approved these changes Jan 22, 2026
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I cherry-picked this commit in the #18986 branch and now the quantize KV cache tests are also passing:

Details 
ggml_cuda_init: found 1 CUDA devices:
  Device 0: NVIDIA GB10, compute capability 12.1, VMM: yes
ggml_backend_cuda_get_available_uma_memory: final available_memory_kb: 121232112
record_update: disabling CUDA graphs due to too many consecutive updates
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=1,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=1,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=3,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=32,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f32,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=f16,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q8_0,permute=[0,2,1,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,1,2,3]): OK
  FLASH_ATTN_EXT(hsk=576,hsv=512,nh=4,nr23=[4,1],kv=512,nb=35,mask=1,sinks=0,max_bias=0.000000,logit_softcap=0.000000,prec=f32,type_KV=q4_0,permute=[0,2,1,3]): OK
  Backend CUDA0: OK

@github-actions github-actions Bot added Nvidia GPU Issues specific to Nvidia GPUs ggml changes relating to the ggml tensor library for machine learning labels Jan 22, 2026
@JohannesGaessler JohannesGaessler merged commit e2baf02 into ggml-org:master Jan 22, 2026
77 of 78 checks passed
ronaldmannak pushed a commit to PicoMLX/llama.cpp that referenced this pull request Jan 24, 2026
@JohannesGaessler @ronaldmannak
CUDA: fix alignment check for FA (ggml-org#19023)
3a1946d
ronaldmannak pushed a commit to PicoMLX/llama.cpp that referenced this pull request Jan 24, 2026
@JohannesGaessler @ronaldmannak
CUDA: fix alignment check for FA (ggml-org#19023)
ebfddbc
shaofeiqi pushed a commit to qualcomm/llama.cpp that referenced this pull request Feb 6, 2026
@JohannesGaessler @shaofeiqi
CUDA: fix alignment check for FA (ggml-org#19023)
b6f9753
Seunghhon pushed a commit to Seunghhon/llama.cpp that referenced this pull request Apr 26, 2026
@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
c74448f
ljubomirj pushed a commit to ljubomirj/llama.cpp that referenced this pull request May 6, 2026
@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
6943159
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@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
7311ea3
my-other-github-account pushed a commit to my-other-github-account/llama.cpp that referenced this pull request May 15, 2026
@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
9b87ec0
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@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
e04712e
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@JohannesGaessler
CUDA: fix alignment check for FA (ggml-org#19023)
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