NVIDIA: SAUCE: vfio/nvgrace-egm: Add null pointer checks after memory allocations

Add missing null pointer checks after vzalloc() calls in the NVIDIA
Grace GPU driver's EGM (External GPU Memory) handling code. This
prevents potential null pointer dereferences in the memory failure
handling and bad page fetching functions, providing proper error
handling for allocation failures.

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 63127e2 https://github.com/NVIDIA/NV-Kernels/tree/24.04_linux-nvidia-adv-6.11-next)
Signed-off-by: Nirmoy Das <nirmoyd@nvidia.com>

Author: KobaKoNvidia

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

@@ -62,6 +62,8 @@ nvgrace_egm_pfn_memory_failure(struct pfn_address_space *pfn_space,
 	 * MM has called to notify a poisoned page. Track that in the hastable.
 	 */
 	ecc = (struct h_node *)(vzalloc(sizeof(struct h_node)));
+	if (!ecc)
+		return;  /* Silently fail on allocation error */
 	ecc->mem_offset = mem_offset;
 	hash_add(region->htbl, &ecc->node, ecc->mem_offset);
 }
@@ -349,6 +351,8 @@ static void nvgrace_egm_fetch_bad_pages(struct pci_dev *pdev,
 		 * apps.
 		 */
 		retired_page = (struct h_node *)(vzalloc(sizeof(struct h_node)));
+		if (!retired_page)
+			continue;  /* Skip this entry on allocation failure */
 		retired_page->mem_offset = *((u64 *)memaddr + index + 1) -
 					   region->egmphys;
 		hash_add(region->htbl, &retired_page->node, retired_page->mem_offset);