Re: [PATCH i-g-t 2/4] lib/gpgpu_shader: Add causing a read pagefault from the eu thread

[Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>]

On 11/19/24 1:38 PM, Manszewski, Christoph wrote:
> Hi Gwan-gyeong,
> 
> On 15.11.2024 15:11, Gwan-gyeong Mun wrote:
>> Create a function that causing a read pagefault using the eu thread load
>> instruction. If the given ppgtt address points to an unallocated ppgtt
>> virtual address,  this shader can cause a read pagefault.
>> To directly use a 64-bit address as an argument, use the
>> Untyped 2D Block Array Load Instruction.
>>
>> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
>> ---
>>   lib/gpgpu_shader.c          | 92 +++++++++++++++++++++++++++++++++++++
>>   lib/gpgpu_shader.h          |  1 +
>>   lib/iga64_generated_codes.c | 21 ++++++++-
>>   3 files changed, 113 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/gpgpu_shader.c b/lib/gpgpu_shader.c
>> index 7a2f0d28d..d7c47be80 100644
>> --- a/lib/gpgpu_shader.c
>> +++ b/lib/gpgpu_shader.c
>> @@ -912,3 +912,95 @@ void 
>> gpgpu_shader__end_system_routine_step_if_eq(struct gpgpu_shader *shdr,
>>       ", 0x807fffff, /* leave breakpoint exception */
>>       y_offset, value, 0x7fffff /* clear all exceptions */ );
>>   }
>> +
>> +/**
>> + * gpgpu_shader__read_page_fault:
>> + * @shdr: shader to be modified
>> + * @ppgtt_addr: ppgtt virtual address to raise pagefault
>> + *
>> + * For a given arbitrary ppgtt virtual address, it raises a pagefault 
>> using
>> + * the eu thread load instruction.
>> + */
>> +void gpgpu_shader__read_page_fault(struct gpgpu_shader *shdr, 
>> uint64_t ppgtt_addr)
> 
> I admit I haven't read much into the assembly however a question about 
> the naming and intention of this function comes to mind - why does this 
> function carry the "read_page_fault" suffix? Isn't this supposed to be a 
> complementary "read" function to the previously introduced 
> "gpgpu_shader__write_offset" function?
As I mentioned in another email reply, I'm going to change the naming of 
these functions.
> 
> It seems as if they both should just allow to read/write a specified 
> ppgtt address and if it isn't bound then a page fault will occur. If 
> that is the case I would suggest to use some matching naming, like 
> "__write_ppgtt_offset/__read_ppgtt_offset" or some variation of what 
> Andrzej suggested.
> 
> Thanks,
> Christoph
> 
>> +{
>> +    /* pagefault ppgtt virtual address */
>> +    uint64_t addr = CANONICAL(ppgtt_addr);
>> +
>> +    igt_assert_f((addr & 0x3) == 0, "address must be aligned to 
>> DWord!\n");
>> +
>> +    emit_iga64_code(shdr, read_page_fault, "                \n\
>> +#if GEN_VER >= 2000                                \n\
>> +// Unyped 2D Block Array Load                             \n\
>> +// Instruction_Load2DBlockArray                            \n\
>> +// bspec: 63972                                    \n\
>> +// src0 address payload (Untyped2DBLOCKAddressPayload) specifies 
>> both        \n\
>> +//    the block parameters and the 2D Surface parameters.            \n\
>> +// Untyped2DBLOCKAddressPayload                            \n\
>> +// bspec: 63986                                    \n\
>> +// [243:240] Array Length: 0 (length is 1)                    \n\
>> +// [239:232] Block Height: 0 (height is 1)                    \n\
>> +// [231:224] Block Width: 0xf (width is 16)                    \n\
>> +// [223:192] Block Start Y: 0                            \n\
>> +// [191:160] Block Start X: 0                            \n\
>> +// [159:128] Untyped 2D Surface Pitch: 0x3f (pitch is 64 
>> bytes)            \n\
>> +// [127:96] Untyped 2D Surface Height: 0 (height is 1)                
>> \n\
>> +// [95:64] Untyped 2D Surface Width: 0x3f (width is 64 
>> bytes)            \n\
>> +// [63:0] Untyped 2D Surface Base Address                    \n\
>> +// initialize register                                \n\
>> +(W)    mov (8)            r30.0<1>:uq    0x0:uq                \n\
>> +// [0:31] Untyped 2D Surface Base Address low                    \n\
>> +(W)    mov (1)            r30.0<1>:ud    ARG(0):ud            \n\
>> +// [32:63] Untyped 2D Surface Base Address high                    \n\
>> +(W)    mov (1)            r30.1<1>:ud ARG(1):ud                \n\
>> +// [95:64] Untyped 2D Surface Width: 0x3f                    \n\
>> +//       (Width minus 1 (in bytes) of the 2D surface, it represents 
>> 64)    \n\
>> +(W)    mov (1)         r30.2<1>:ud    0x3f:ud                \n\
>> +// [127:96] Untyped 2D Surface Height: 0x0                    \n\
>> +//        (Height minus 1 (in number of data elements) of            \n\
>> +//        the Untyped 2D surface, it represents 1)                \n\
>> +(W)    mov (1)         r30.3<1>:ud    0x0:ud                \n\
>> +// [159:128] Untyped 2D Surface Pitch: 0x3f                    \n\
>> +//         (Pitch minus 1 (in bytes) of the 2D surface, it represents 
>> 64)    \n\
>> +(W)    mov (1)            r30.4<1>:ud    0x3f:ud                \n\
>> +// [231:224] Block Width: 0xf (15)                        \n\
>> +//         (Specifies the width minus 1 (in number of data elements) 
>> for this    \n\
>> +//         rectangular region, it represents 16)                \n\
>> +// Block width (encoded_value + 1) must be a multiple of DW (4 
>> bytes).        \n\
>> +// [239:232] Block Height: 0                            \n\
>> +//         (Specifies the height minus 1 (in number of data elements) 
>> for    \n\
>> +//         this rectangular region, it represents 1)                \n\
>> +// [243:240] Array Length: 0                            \n\
>> +//         (Specifies Array Length minus 1 for Load2DBlockArray 
>> messages,    \n\
>> +//         must be zero for 2D Block Store messages, it represents 
>> 1)        \n\
>> +(W)    mov (1)            r30.7<1>:ud    0xf:ud                \n\
>> +//                                        \n\
>> +// dest data payload format is selected by Data Size.                \n\
>> +// Block Height x Block Width x Data size / GRF Register 
>> size            \n\
>> +//    => 1 x 16 x 32bit / 512bit = 1                        \n\
>> +// data payload format size is 1 GRF Register.                    \n\
>> +//                                        \n\
>> +// send.ugm Untyped 2D Block Array Load                        \n\
>> +// Format: send.ugm (1) dst src0 src1 ExtMsg MsgDesc                \n\
>> +// Execution Mask restriction: SIMT1                        \n\
>> +//                                        \n\
>> +// Extended Message Descriptor (Dataport Extended Descriptor Imm 2D 
>> Block)    \n\
>> +// bspec: 67780                                    \n\
>> +// 0x0 =>                                    \n\
>> +// [32:22] Global Y_offset: 0                            \n\
>> +// [21:12] Global X_offset: 0                            \n\
>> +//                                        \n\
>> +// Message Descriptor                                \n\
>> +// bspec: 63972                                    \n\
>> +// 0x2128403 =>                                    \n\
>> +// [30:29] Address Type: 0 (FLAT)                        \n\
>> +// [28:25] Src0 Length: 1                            \n\
>> +// [24:20] Dest Length: 1                            \n\
>> +// [19:16] Cache : 2 (L1UC_L3UC) 10                        \n\
>> +// [15] Transpose Block: 1                            \n\
>> +// [11:9] Data Size: 2 (D32) 10                            \n\
>> +// [7] VNNI Transform: 0                            \n\
>> +// [5:0] Load Operation: 3 (Load 2D Block) 11                    \n\
>> +(W)    send.ugm (1)        r31    r30    null    0x0    0x2128403    \n\
>> +#endif                                        \n\
>> +    ", lower_32_bits(addr), upper_32_bits(addr));
>> +}
>> \ No newline at end of file
>> diff --git a/lib/gpgpu_shader.h b/lib/gpgpu_shader.h
>> index 355b128b5..318550c52 100644
>> --- a/lib/gpgpu_shader.h
>> +++ b/lib/gpgpu_shader.h
>> @@ -87,6 +87,7 @@ void gpgpu_shader__write_offset(struct gpgpu_shader 
>> *shdr, uint64_t ppgtt_offset
>>                   uint32_t value);
>>   void gpgpu_shader__write_on_exception(struct gpgpu_shader *shdr, 
>> uint32_t dw, uint32_t x_offset,
>>                         uint32_t y_offset, uint32_t mask, uint32_t 
>> value);
>> +void gpgpu_shader__read_page_fault(struct gpgpu_shader *shdr, 
>> uint64_t ppgtt_addr);
>>   void gpgpu_shader__label(struct gpgpu_shader *shdr, int label_id);
>>   void gpgpu_shader__jump(struct gpgpu_shader *shdr, int label_id);
>>   void gpgpu_shader__jump_neq(struct gpgpu_shader *shdr, int label_id,
>> diff --git a/lib/iga64_generated_codes.c b/lib/iga64_generated_codes.c
>> index b23613ac4..53a705358 100644
>> --- a/lib/iga64_generated_codes.c
>> +++ b/lib/iga64_generated_codes.c
>> @@ -3,7 +3,7 @@
>>   #include "gpgpu_shader.h"
>> -#define MD5_SUM_IGA64_ASMS 4fcde43dedb9d3212f1d85b5b180b0c1
>> +#define MD5_SUM_IGA64_ASMS 01290b5ecda7a6e765463558d6f59952
>>   struct iga64_template const iga64_code_gpgpu_fill[] = {
>>       { .gen_ver = 2000, .size = 44, .code = (const uint32_t []) {
>> @@ -79,6 +79,25 @@ struct iga64_template const iga64_code_gpgpu_fill[] 
>> = {
>>       }}
>>   };
>> +struct iga64_template const iga64_code_read_page_fault[] = {
>> +    { .gen_ver = 2000, .size = 44, .code = (const uint32_t []) {
>> +        0x800c0061, 0x1e054330, 0x00000000, 0x00000000,
>> +        0x80000061, 0x1e054220, 0x00000000, 0xc0ded000,
>> +        0x80000061, 0x1e154220, 0x00000000, 0xc0ded001,
>> +        0x80000061, 0x1e254220, 0x00000000, 0x0000003f,
>> +        0x80000061, 0x1e354220, 0x00000000, 0x00000000,
>> +        0x80000061, 0x1e454220, 0x00000000, 0x0000003f,
>> +        0x80000061, 0x1e754220, 0x00000000, 0x0000000f,
>> +        0x80032031, 0x1f0c0000, 0xf8061e0c, 0x00a00000,
>> +        0x80000001, 0x00010000, 0x20000000, 0x00000000,
>> +        0x80000001, 0x00010000, 0x30000000, 0x00000000,
>> +        0x80000901, 0x00010000, 0x00000000, 0x00000000,
>> +    }},
>> +    { .gen_ver = 0, .size = 0, .code = (const uint32_t []) {
>> +
>> +    }}
>> +};
>> +
>>   struct iga64_template const 
>> iga64_code_end_system_routine_step_if_eq[] = {
>>       { .gen_ver = 2000, .size = 44, .code = (const uint32_t []) {
>>           0x80000966, 0x80018220, 0x02008000, 0x00008000,