arm64/machdep: Reserve memory when we find Linux EFI reserved memory table

When Linux loads a new kernel via kexec, somtiems it must reserve memory
for devices that are still active (and typically can't be reset or
shutdown). When present, this table is a linked list of ranges that are
still in use that the OS must avoid using.

Mark these areas as reserved.

This is part of the GICv3 workaround code where we must use the PA
addresses already programmed into the GICv3 when we take over. This part
ensure we don't allocate the mmeory for anything else.

Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D37440

sys/arm64/arm64/machdep.c

@@ -580,6 +580,115 @@ print_efi_map_entries(struct efi_map_header *efihdr)
 	foreach_efi_map_entry(efihdr, print_efi_map_entry, NULL);
 }
 
+/*
+ * Map the passed in VA in EFI space to a void * using the efi memory table to
+ * find the PA and return it in the DMAP, if it exists. We're used between the
+ * calls to pmap_bootstrap() and physmem_init_kernel_globals() to parse CFG
+ * tables We assume that either the entry you are mapping fits within its page,
+ * or if it spills to the next page, that's contiguous in PA and in the DMAP.
+ * All observed tables obey the first part of this precondition.
+ */
+struct early_map_data
+{
+	vm_offset_t va;
+	vm_offset_t pa;
+};
+
+static void
+efi_early_map_entry(struct efi_md *p, void *argp)
+{
+	struct early_map_data *emdp = argp;
+	vm_offset_t s, e;
+
+	if (emdp->pa != 0)
+		return;
+	if ((p->md_attr & EFI_MD_ATTR_RT) == 0)
+		return;
+	s = p->md_virt;
+	e = p->md_virt + p->md_pages * EFI_PAGE_SIZE;
+	if (emdp->va < s  || emdp->va >= e)
+		return;
+	emdp->pa = p->md_phys + (emdp->va - p->md_virt);
+}
+
+static void *
+efi_early_map(vm_offset_t va)
+{
+	struct early_map_data emd = { .va = va };
+
+	foreach_efi_map_entry(efihdr, efi_early_map_entry, &emd);
+	if (emd.pa == 0)
+		return NULL;
+	return (void *)PHYS_TO_DMAP(emd.pa);
+}
+
+
+/*
+ * When booted via kboot, the prior kernel will pass in reserved memory areas in
+ * a EFI config table. We need to find that table and walk through it excluding
+ * the memory ranges in it. btw, this is called too early for the printf to do
+ * anything since msgbufp isn't initialized, let alone a console...
+ */
+static void
+exclude_efi_memreserve(vm_offset_t efi_systbl_phys)
+{
+	struct efi_systbl *systbl;
+	struct uuid efi_memreserve = LINUX_EFI_MEMRESERVE_TABLE;
+
+	systbl = (struct efi_systbl *)PHYS_TO_DMAP(efi_systbl_phys);
+	if (systbl == NULL) {
+		printf("can't map systbl\n");
+		return;
+	}
+	if (systbl->st_hdr.th_sig != EFI_SYSTBL_SIG) {
+		printf("Bad signature for systbl %#lx\n", systbl->st_hdr.th_sig);
+		return;
+	}
+
+	/*
+	 * We don't yet have the pmap system booted enough to create a pmap for
+	 * the efi firmware's preferred address space from the GetMemoryMap()
+	 * table. The st_cfgtbl is a VA in this space, so we need to do the
+	 * mapping ourselves to a kernel VA with efi_early_map. We assume that
+	 * the cfgtbl entries don't span a page. Other pointers are PAs, as
+	 * noted below.
+	 */
+	if (systbl->st_cfgtbl == 0)	/* Failsafe st_entries should == 0 in this case */
+		return;
+	for (int i = 0; i < systbl->st_entries; i++) {
+		struct efi_cfgtbl *cfgtbl;
+		struct linux_efi_memreserve *mr;
+
+		cfgtbl = efi_early_map(systbl->st_cfgtbl + i * sizeof(*cfgtbl));
+		if (cfgtbl == NULL)
+			panic("Can't map the config table entry %d\n", i);
+		if (memcmp(&cfgtbl->ct_uuid, &efi_memreserve, sizeof(struct uuid)) != 0)
+			continue;
+
+		/*
+		 * cfgtbl points are either VA or PA, depending on the GUID of
+		 * the table. memreserve GUID pointers are PA and not converted
+		 * after a SetVirtualAddressMap(). The list's mr_next pointer
+		 * is also a PA.
+		 */
+		mr = (struct linux_efi_memreserve *)PHYS_TO_DMAP(
+			(vm_offset_t)cfgtbl->ct_data);
+		while (true) {
+			for (int j = 0; j < mr->mr_count; j++) {
+				struct linux_efi_memreserve_entry *mre;
+
+				mre = &mr->mr_entry[j];
+				physmem_exclude_region(mre->mre_base, mre->mre_size,
+				    EXFLAG_NODUMP | EXFLAG_NOALLOC);
+			}
+			if (mr->mr_next == 0)
+				break;
+			mr = (struct linux_efi_memreserve *)PHYS_TO_DMAP(mr->mr_next);
+		};
+	}
+
+}
+
 #ifdef FDT
 static void
 try_load_dtb(caddr_t kmdp)
@@ -825,6 +934,9 @@ initarm(struct arm64_bootparams *abp)
 	/* Exclude entries needed in the DMAP region, but not phys_avail */
 	if (efihdr != NULL)
 		exclude_efi_map_entries(efihdr);
+	/*  Do the same for reserve entries in the EFI MEMRESERVE table */
+	if (efi_systbl_phys != 0)
+		exclude_efi_memreserve(efi_systbl_phys);
 	physmem_init_kernel_globals();
 
 	devmap_bootstrap(0, NULL);