diff --git a/core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp b/core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp
index 29a657f70..71139e23c 100644
--- a/core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp
+++ b/core/libs/prx/libSceAgcDriver/Graphics/src/GuestBufferMemory.cpp
@@ -29,6 +29,7 @@
 #include <set>
 #include <thread>
 #include <stop_token>
+#include <cerrno>
 #include <cstdlib>
 #include <cstdio>
 #include <chrono>
@@ -239,7 +240,15 @@ const char* createHostPointerImport(const Context& context, HostImport& entry, V
 
 #ifndef _WIN32
 int udmabufDevice() {
-    static const int device = open("/dev/udmabuf", O_RDWR | O_CLOEXEC);
+    static const int device = [] {
+        const int result = open("/dev/udmabuf", O_RDWR | O_CLOEXEC);
+        if (result < 0) {
+            const int error = errno;
+            std::fprintf(stderr, "[gpu] open /dev/udmabuf: %s; shared direct memory is copied instead of imported, and GPU stores through FLAT/GLOBAL addresses do not reach it%s\n",
+                std::strerror(error), error == EACCES ? " (give the user read-write access to /dev/udmabuf, for example through the kvm group)" : "");
+        }
+        return result;
+    }();
     return device;
 }
 
diff --git a/docs/user/USAGE.md b/docs/user/USAGE.md
index ba4f6d352..6fbc05f4a 100644
--- a/docs/user/USAGE.md
+++ b/docs/user/USAGE.md
@@ -83,6 +83,8 @@ On Windows, a self-built `libs/` also needs `libgcc_s_seh-1.dll`, `libstdc++-6.d
 
 On Windows, direct memory (`sceKernelAllocateDirectMemory`, up to 13824 MiB per title) is committed in full when the title allocates it, not when its pages are first used. The system commit limit (installed memory plus page file size, the second value of Committed in Task Manager) must cover it together with all other committed memory. Otherwise the allocation throws `create direct memory backing of 0x<n> bytes (<m> MiB)` with the Windows error; enlarge the page file or close other applications.
 
+On Linux, when the Vulkan driver imports dma-buf memory (not the NVIDIA proprietary driver), shared direct memory is imported through `/dev/udmabuf`, and the user who runs the game needs read-write access to it. Many distributions create it as `root:kvm` with mode `0660`: add the user to the `kvm` group and log in again (an ACL such as `setfacl -m u:$USER:rw /dev/udmabuf` lasts until the next reboot). Without access, startup prints `[gpu] open /dev/udmabuf: Permission denied`, these ranges are copied instead of imported, and GPU stores to them through FLAT/GLOBAL addresses fail with `BDA access failed`. Ranges above udmabuf's `size_limit_mb` (64 MiB by default) are copied as well.
+
 Linux:
 
 ```sh