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zeVirtualMemMap of one physical object into a second VA range returns SUCCESS, then access through it gives ZE_RESULT_ERROR_DEVICE_LOST (Arc Pro B60)

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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
15/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
cpp
Ambito
hpc

Direzione di ricerca

The payload names no source files, only the standalone repro l0_alias_repro.cpp and the calls zeVirtualMemMap, zePhysicalMemCreate and zeCommandListAppendMemoryCopy. Build the repro against the Level Zero loader and confirm the 0x70000001 result on the second range. Done means a decision on whether the second map should fail or the alias should work, which the thread has not yet made. This is driver memory-management work and needs maintainer input before any change.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Moved from oneapi-src/level-zero#536 at the maintainers' request.

Summary
Mapping the same ze_physical_mem_handle_t into two reserved virtual ranges succeeds (both zeVirtualMemMap calls return ZE_RESULT_SUCCESS). A write through the first range completes, but the first access through the second range fails with ZE_RESULT_ERROR_DEVICE_LOST (0x70000001). From SYCL/PyTorch kernels the same access hangs instead. The spec does not say a physical object may be mapped only once, so either the second map should fail, or the alias should work.

Repro (single file, l0_alias_repro.cpp):

l0_alias_repro.cpp 
// Level Zero: one physical memory object mapped into two virtual ranges.
// Writes through range A, then reads through range B with an immediate command list.
// Build: g++ -O1 l0_alias_repro.cpp -I/usr/local/include -L/usr/local/lib -lze_loader -o l0_alias_repro
#include <level_zero/ze_api.h>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>

#define CHECK(call)                                                       \
  do {                                                                    \
    ze_result_t r = (call);                                               \
    if (r != ZE_RESULT_SUCCESS) {                                         \
      std::printf("%s failed: 0x%x\n", #call, (unsigned)r);              \
      std::exit(1);                                                       \
    }                                                                     \
  } while (0)

int main() {
  CHECK(zeInit(ZE_INIT_FLAG_GPU_ONLY));
  uint32_t n = 1;
  ze_driver_handle_t driver;
  CHECK(zeDriverGet(&n, &driver));
  n = 1;
  ze_device_handle_t device;
  CHECK(zeDeviceGet(driver, &n, &device));
  ze_context_desc_t ctx_desc = {ZE_STRUCTURE_TYPE_CONTEXT_DESC, nullptr, 0};
  ze_context_handle_t ctx;
  CHECK(zeContextCreate(driver, &ctx_desc, &ctx));

  size_t page = 0;
  CHECK(zeVirtualMemQueryPageSize(ctx, device, 2 << 20, &page));
  ze_physical_mem_desc_t pdesc = {ZE_STRUCTURE_TYPE_PHYSICAL_MEM_DESC, nullptr, 0, page};
  ze_physical_mem_handle_t phys;
  CHECK(zePhysicalMemCreate(ctx, device, &pdesc, &phys));

  void *va_a = nullptr, *va_b = nullptr;
  CHECK(zeVirtualMemReserve(ctx, nullptr, page, &va_a));
  CHECK(zeVirtualMemReserve(ctx, nullptr, page, &va_b));
  CHECK(zeVirtualMemMap(ctx, va_a, page, phys, 0, ZE_MEMORY_ACCESS_ATTRIBUTE_READWRITE));
  CHECK(zeVirtualMemMap(ctx, va_b, page, phys, 0, ZE_MEMORY_ACCESS_ATTRIBUTE_READWRITE));
  std::printf("page=%zu va_a=%p va_b=%p: both maps returned SUCCESS\n", page, va_a, va_b);

  ze_command_queue_desc_t qdesc = {ZE_STRUCTURE_TYPE_COMMAND_QUEUE_DESC, nullptr, 0, 0, 0,
                                   ZE_COMMAND_QUEUE_MODE_ASYNCHRONOUS, ZE_COMMAND_QUEUE_PRIORITY_NORMAL};
  ze_command_list_handle_t list;
  CHECK(zeCommandListCreateImmediate(ctx, device, &qdesc, &list));

  std::vector<unsigned char> src(page, 0x5a), dst(page, 0);
  CHECK(zeCommandListAppendMemoryCopy(list, va_a, src.data(), page, nullptr, 0, nullptr));
  CHECK(zeCommandListHostSynchronize(list, UINT64_MAX));
  std::printf("write through va_a: done\n");
  std::fflush(stdout);

  CHECK(zeCommandListAppendMemoryCopy(list, dst.data(), va_b, page, nullptr, 0, nullptr));
  // 10 s timeout: on Arc Pro B60 this read never completes
  ze_result_t r = zeCommandListHostSynchronize(list, 10ull * 1000 * 1000 * 1000);
  std::printf("read through va_b: result=0x%x, data %s\n", (unsigned)r,
              r == ZE_RESULT_SUCCESS ? (std::memcmp(src.data(), dst.data(), page) ? "WRONG" : "ok")
                                     : "not available");
  return r == ZE_RESULT_SUCCESS ? 0 : 2;
}

g++ -O1 l0_alias_repro.cpp -I/usr/local/include -L/usr/local/lib -lze_loader -o l0_alias_repro
ZE_AFFINITY_MASK=0 ./l0_alias_repro

Output:

page=2097152 va_a=0x7af6a2000000 va_b=0x7af6a1c00000: both maps returned SUCCESS
write through va_a: done
zeCommandListAppendMemoryCopy(list, dst.data(), va_b, page, nullptr, 0, nullptr) failed: 0x70000001

Expected: the read through va_b returns the bytes written through va_a (as cuMemMap allows on CUDA), or the second zeVirtualMemMap returns an error.

Environment

  • GPU: Intel Arc Pro B60 (Battlemage G21), xe kernel driver, kernel 6.14.0-37-generic
  • compute-runtime (libze-intel-gpu1): 26.18.38308.1
  • Level Zero loader: 1.28.0
  • OS: Ubuntu 25.04

Impact: SGLang's DWDP (expert-weight prefetch for MoE) has to unmap and remap pool pages before every layer on Level Zero instead of aliasing them, which costs a host synchronisation per layer (sgl-project/sglang#40763).

Lingua principale
C++
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