Fix new users of MAXPHYS and hide it from the kernel namespace

In cd85379104, kib made maxphys a load-time tunable.  This made
the #define MAXPHYS in sys/param.h  almost entirely obsolete, as
it could now be overridden by kern.maxphys at boot time, or by
opt_maxphys.h.

However, decades of tradition have led to several new, incorrect, uses
of MAXPHYS in other parts of the kernel, mostly by seasoned
developers.  I've corrected those uses here in a mechanical fashion,
and verified that it fixes a bug in the md driver that I was
experiencing.

Since using MAXPHYS is such an easy mistake to make, it is best to
hide it from the kernel namespace.  So I've moved its definition to
_maxphys.h, which is now included in param.h only for userspace.

That brings up the fact that lots of userspace programs use MAXPHYS
for different reasons, most of them probably wrong.  Userspace consumers
that really need to know the value of maxphys should probably be
changed to use the kern.maxphys sysctl.  But that's outside the scope
of this change.

Reviewed by: imp, jkim, kib, markj
Fixes: 30038a8b4e ("md: Get rid of the pbuf zone")
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D44986

sys/compat/linux/linux_socket.c

@@ -2468,7 +2468,7 @@ sendfile_fallback(struct thread *td, struct file *fp, l_int out,
 		out_offset = 0;
 
 	flags = FOF_OFFSET | FOF_NOUPDATE;
-	bufsz = min(count, MAXPHYS);
+	bufsz = min(count, maxphys);
 	buf = malloc(bufsz, M_LINUX, M_WAITOK);
 	bytes_sent = 0;
 	while (bytes_sent < count) {

sys/dev/md/md.c

@@ -965,7 +965,7 @@ mdstart_vnode(struct md_s *sc, struct bio *bp)
 		    PAGE_MASK))));
 		iolen = min(ptoa(npages) - (ma_offs & PAGE_MASK), len);
 		KASSERT(iolen > 0, ("zero iolen"));
-		KASSERT(npages <= atop(MAXPHYS + PAGE_SIZE),
+		KASSERT(npages <= atop(maxphys + PAGE_SIZE),
 		    ("npages %d too large", npages));
 		pmap_qenter(sc->kva, &bp->bio_ma[atop(ma_offs)], npages);
 		aiov.iov_base = (void *)(sc->kva + (ma_offs & PAGE_MASK));
@@ -1487,7 +1487,7 @@ mdcreate_vnode(struct md_s *sc, struct md_req *mdr, struct thread *td)
 		goto bad;
 	}
 
-	sc->kva = kva_alloc(MAXPHYS + PAGE_SIZE);
+	sc->kva = kva_alloc(maxphys + PAGE_SIZE);
 	return (0);
 bad:
 	VOP_UNLOCK(nd.ni_vp);
@@ -1547,7 +1547,7 @@ mddestroy(struct md_s *sc, struct thread *td)
 	if (sc->uma)
 		uma_zdestroy(sc->uma);
 	if (sc->kva)
-		kva_free(sc->kva, MAXPHYS + PAGE_SIZE);
+		kva_free(sc->kva, maxphys + PAGE_SIZE);
 
 	LIST_REMOVE(sc, list);
 	free_unr(md_uh, sc->unit);

sys/dev/rtsx/rtsx.c

@@ -311,7 +311,7 @@ static int	rtsx_resume(device_t dev);
 #define	RTSX_DMA_ALIGN		4
 #define	RTSX_HOSTCMD_MAX	256
 #define	RTSX_DMA_CMD_BIFSIZE	(sizeof(uint32_t) * RTSX_HOSTCMD_MAX)
-#define	RTSX_DMA_DATA_BUFSIZE	MAXPHYS
+#define	RTSX_DMA_DATA_BUFSIZE	maxphys
 
 #define	ISSET(t, f) ((t) & (f))
 
@@ -2762,7 +2762,7 @@ rtsx_xfer(struct rtsx_softc *sc, struct mmc_command *cmd)
 			      (unsigned long)cmd->data->len, (unsigned long)cmd->data->xfer_len);
 
 	if (cmd->data->len > RTSX_DMA_DATA_BUFSIZE) {
-		device_printf(sc->rtsx_dev, "rtsx_xfer() length too large: %ld > %d\n",
+		device_printf(sc->rtsx_dev, "rtsx_xfer() length too large: %ld > %ld\n",
 			      (unsigned long)cmd->data->len, RTSX_DMA_DATA_BUFSIZE);
 		cmd->error = MMC_ERR_INVALID;
 		return (MMC_ERR_INVALID);

sys/kern/subr_param.c

@@ -41,6 +41,7 @@
 #include "opt_maxusers.h"
 
 #include <sys/param.h>
+#include <sys/_maxphys.h>
 #include <sys/systm.h>
 #include <sys/buf.h>
 #include <sys/kernel.h>

sys/sys/_maxphys.h

@@ -0,0 +1,10 @@
+/*-
+ * This file is in the public domain.
+ */
+#ifndef MAXPHYS
+#ifdef __ILP32__
+#define MAXPHYS		(128 * 1024)
+#else
+#define MAXPHYS		(1024 * 1024)
+#endif
+#endif

sys/sys/param.h

@@ -161,6 +161,7 @@
 #include <machine/param.h>
 #ifndef _KERNEL
 #include <sys/limits.h>
+#include <sys/_maxphys.h>
 #endif
 
 #ifndef DEV_BSHIFT
@@ -174,13 +175,6 @@
 #ifndef DFLTPHYS
 #define DFLTPHYS	(64 * 1024)	/* default max raw I/O transfer size */
 #endif
-#ifndef MAXPHYS				/* max raw I/O transfer size */
-#ifdef __ILP32__
-#define MAXPHYS		(128 * 1024)
-#else
-#define MAXPHYS		(1024 * 1024)
-#endif
-#endif
 #ifndef MAXDUMPPGS
 #define MAXDUMPPGS	(DFLTPHYS/PAGE_SIZE)
 #endif