From 18ce865a4ffdb2a794fe012c81d7eb00f9a40104 Mon Sep 17 00:00:00 2001
From: Oleksandr Tymoshenko <gonzo@FreeBSD.org>
Date: Thu, 3 Dec 2020 05:39:27 +0000
Subject: [PATCH] Add support for hw.physmem tunable for ARM/ARM64/RISC-V
 platforms

hw.physmem tunable allows to limit number of physical memory available to the
system. It's handled in machdep files for x86 and PowerPC. This patch adds
required logic to the consolidated physmem management interface that is used by
ARM, ARM64, and RISC-V.

Submitted by:	Klara, Inc.
Reviewed by:	mhorne
Sponsored by:	Ampere Computing
Differential Revision:	https://reviews.freebsd.org/D27152
---
 sys/kern/subr_physmem.c | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/sys/kern/subr_physmem.c b/sys/kern/subr_physmem.c
index 469a29ffde75..ea1ec12dd065 100644
--- a/sys/kern/subr_physmem.c
+++ b/sys/kern/subr_physmem.c
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/kernel.h>
 #include <sys/physmem.h>
 #include <vm/vm.h>
 #include <vm/vm_param.h>
@@ -141,6 +142,10 @@ physmem_print_tables(void)
 /*
  * Walk the list of hardware regions, processing it against the list of
  * exclusions that contain the given exflags, and generating an "avail list".
+ * 
+ * If maxphyssz is not zero it sets upper limit, in bytes, for the total
+ * "avail list" size. Walk stops once the limit is reached and the last region
+ * is cut short if necessary.
  *
  * Updates the value at *pavail with the sum of all pages in all hw regions.
  *
@@ -148,15 +153,17 @@ physmem_print_tables(void)
  */
 static size_t
 regions_to_avail(vm_paddr_t *avail, uint32_t exflags, size_t maxavail,
-    long *pavail, long *prealmem)
+    uint64_t maxphyssz, long *pavail, long *prealmem)
 {
 	size_t acnt, exi, hwi;
 	uint64_t end, start, xend, xstart;
 	long availmem, totalmem;
 	const struct region *exp, *hwp;
+	uint64_t availsz;
 
 	totalmem = 0;
 	availmem = 0;
+	availsz = 0;
 	acnt = 0;
 	for (hwi = 0, hwp = hwregions; hwi < hwcnt; ++hwi, ++hwp) {
 		start = hwp->addr;
@@ -202,6 +209,13 @@ regions_to_avail(vm_paddr_t *avail, uint32_t exflags, size_t maxavail,
 			 * could affect the remainder of this hw region.
 			 */
 			if ((xstart > start) && (xend < end)) {
+
+				if ((maxphyssz != 0) &&
+				    (availsz + xstart - start > maxphyssz)) {
+					xstart = maxphyssz + start - availsz;
+				}
+				if (xstart <= start)
+					continue;
 				if (acnt > 0 &&
 				    avail[acnt - 1] == (vm_paddr_t)start) {
 					avail[acnt - 1] = (vm_paddr_t)xstart;
@@ -209,6 +223,7 @@ regions_to_avail(vm_paddr_t *avail, uint32_t exflags, size_t maxavail,
 					avail[acnt++] = (vm_paddr_t)start;
 					avail[acnt++] = (vm_paddr_t)xstart;
 				}
+				availsz += (xstart - start);
 				availmem += atop((vm_offset_t)(xstart - start));
 				start = xend;
 				continue;
@@ -228,12 +243,20 @@ regions_to_avail(vm_paddr_t *avail, uint32_t exflags, size_t maxavail,
 		 * available entry for it.
 		 */
 		if (end > start) {
+			if ((maxphyssz != 0) &&
+			    (availsz + end - start > maxphyssz)) {
+				end = maxphyssz + start - availsz;
+			}
+			if (end <= start)
+				break;
+
 			if (acnt > 0 && avail[acnt - 1] == (vm_paddr_t)start) {
 				avail[acnt - 1] = (vm_paddr_t)end;
 			} else {
 				avail[acnt++] = (vm_paddr_t)start;
 				avail[acnt++] = (vm_paddr_t)end;
 			}
+			availsz += end - start;
 			availmem += atop((vm_offset_t)(end - start));
 		}
 		if (acnt >= maxavail)
@@ -362,7 +385,7 @@ size_t
 physmem_avail(vm_paddr_t *avail, size_t maxavail)
 {
 
-	return (regions_to_avail(avail, EXFLAG_NOALLOC, maxavail, NULL, NULL));
+	return (regions_to_avail(avail, EXFLAG_NOALLOC, maxavail, 0, NULL, NULL));
 }
 
 /*
@@ -378,11 +401,15 @@ void
 physmem_init_kernel_globals(void)
 {
 	size_t nextidx;
+	u_long hwphyssz;
 
-	regions_to_avail(dump_avail, EXFLAG_NODUMP, PHYS_AVAIL_ENTRIES, NULL,
-	    NULL);
+	hwphyssz = 0;
+	TUNABLE_ULONG_FETCH("hw.physmem", &hwphyssz);
+
+	regions_to_avail(dump_avail, EXFLAG_NODUMP, PHYS_AVAIL_ENTRIES,
+	    hwphyssz, NULL, NULL);
 	nextidx = regions_to_avail(phys_avail, EXFLAG_NOALLOC,
-	    PHYS_AVAIL_ENTRIES, &physmem, &realmem);
+	    PHYS_AVAIL_ENTRIES, hwphyssz, &physmem, &realmem);
 	if (nextidx == 0)
 		panic("No memory entries in phys_avail");
 	Maxmem = atop(phys_avail[nextidx - 1]);