NVIDIA: SAUCE: vfio/nvgrace-egm: expose the egm size through sysfs

To allocate the EGM, the userspace need to know it's size. Currently,
there is no easy way for the userspace to determine that.

Make nvgrace-egm expose the size through sysfs that can be queried
by the userspace from /sys/devices/virtual/egm/egmX/egm_size.

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Ref: sj24: /home/nvidia/ankita/kernel_patches/0003_vfio_nvgrace-egm_expose_the_egm_size_through_sysfs.patch
Signed-off-by: Koba Ko <kobak@nvidia.com>
Acked-by: Matthew R. Ochs <mochs@nvidia.com>
Acked-by: Carol L. Soto <csoto@nvidia.com>
Signed-off-by: Matthew R. Ochs <mochs@nvidia.com>
(cherry picked from commit dcdcef2 https://github.com/NVIDIA/NV-Kernels/tree/24.04_linux-nvidia-adv-6.11-next)
Signed-off-by: Nirmoy Das <nirmoyd@nvidia.com>

Author: ankita-nv

drivers/vfio/pci/nvgrace-gpu/egm.c

@@ -380,8 +380,19 @@ static ssize_t gpu_devices_show(struct device *dev, struct device_attribute *att
 
 static DEVICE_ATTR_RO(gpu_devices);
 
+static ssize_t egm_size_show(struct device *dev, struct device_attribute *attr,
+                            char *buf)
+{
+       struct egm_region *region =
+               container_of(dev, struct egm_region, device);
+       return sysfs_emit(buf, "0x%lx\n", region->egmlength);
+}
+
+static DEVICE_ATTR_RO(egm_size);
+
 static struct attribute *attrs[] = {
        &dev_attr_gpu_devices.attr,
+       &dev_attr_egm_size.attr,
        NULL,
 };