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Date:      Mon, 18 Dec 2017 09:32:56 +0000 (UTC)
From:      Bruce Evans <bde@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r326929 - head/sys/i386/i386
Message-ID:  <201712180932.vBI9Wua5012050@repo.freebsd.org>
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Author: bde
Date: Mon Dec 18 09:32:56 2017
New Revision: 326929
URL: https://svnweb.freebsd.org/changeset/base/326929

Log:
  Fix the undersupported option KERNLOAD, part 1: fix crashes in locore
  when KERNLOAD is not a multiple of NBPDR (not the default) and PSE is
  enabled (the default if the CPU supports it).  Addresses in PDEs must
  be a multiple of NBPDR in the PSE case, but were not so in the crashing
  case.
  
  KERNLOAD defaults to NBPDR.  NBPDR is 4 MB for !PAE and 2 MB for PAE.
  The default can be changed by editing i386/include/vmparam.h or using
  makeoptions.  It can be changed to less than NBPDR to save real and
  virtual memory at a small cost in time, or to more than NBPDR to waste
  real and virtual memory.  It must be larger than 1 MB and a multiple of
  PAGE_SIZE.  When it is less than NBPDR, it is necessarily not a multiple
  of NBPDR.  This case has much larger bugs which will be fixed in part 2.
  
  The fix is to only use PSE for physical addresses above <KERNLOAD
  rounded _up_ to an NBPDR boundary>.  When the rounding is non-null,
  this leaves part of the kernel not using large pages.  Rounding down
  would avoid this pessimization, but would break setting of PAT bits
  on i/o pages if it goes below 1MB.  Since rounding down always goes
  below 1MB when KERNLOAD < NBPDR and the KERNLOAD > NBPDR case is not
  useful, never round down.
  
  Fix related style bugs (e.g., wrong literal values for NBPDR in comments).
  
  Reviewed by:	kib

Modified:
  head/sys/i386/i386/locore.s
  head/sys/i386/i386/pmap.c

Modified: head/sys/i386/i386/locore.s
==============================================================================
--- head/sys/i386/i386/locore.s	Mon Dec 18 05:29:38 2017	(r326928)
+++ head/sys/i386/i386/locore.s	Mon Dec 18 09:32:56 2017	(r326929)
@@ -668,7 +668,7 @@ over_symalloc:
 no_kernend:
 
 	addl	$PDRMASK,%esi		/* Play conservative for now, and */
-	andl	$~PDRMASK,%esi		/*   ... wrap to next 4M. */
+	andl	$~PDRMASK,%esi		/* ... round up to PDR boundary */
 	movl	%esi,R(KERNend)		/* save end of kernel */
 	movl	%esi,R(physfree)	/* next free page is at end of kernel */
 
@@ -784,7 +784,8 @@ no_kernend:
 
 /*
  * Create an identity mapping for low physical memory, including the kernel.
- * The part of this mapping that covers the first 1 MB of physical memory
+ * The part of this mapping given by the first PDE (for the first 4 MB or 2
+ * MB of physical memory)
  * becomes a permanent part of the kernel's address space.  The rest of this
  * mapping is destroyed in pmap_bootstrap().  Ordinarily, the same page table
  * pages are shared by the identity mapping and the kernel's native mapping.
@@ -815,10 +816,9 @@ no_kernend:
 #endif
 
 /*
- * For the non-PSE case, install PDEs for PTs covering the KVA.
- * For the PSE case, do the same, but clobber the ones corresponding
- * to the kernel (from btext to KERNend) with 4M (2M for PAE) ('PS')
- * PDEs immediately after.
+ * Install PDEs for PTs covering enough kva to bootstrap.  Then for the PSE
+ * case, replace the PDEs whose coverage is strictly within the kernel
+ * (between KERNLOAD (rounded up) and KERNend) by large-page PDEs.
  */
 	movl	R(KPTphys), %eax
 	movl	$KPTDI, %ebx
@@ -828,10 +828,10 @@ no_kernend:
 	je	done_pde
 
 	movl	R(KERNend), %ecx
-	movl	$KERNLOAD, %eax
+	movl	$(KERNLOAD + PDRMASK) & ~PDRMASK, %eax
 	subl	%eax, %ecx
 	shrl	$PDRSHIFT, %ecx
-	movl	$(KPTDI+(KERNLOAD/(1 << PDRSHIFT))), %ebx
+	movl	$KPTDI + ((KERNLOAD + PDRMASK) >> PDRSHIFT), %ebx
 	shll	$PDESHIFT, %ebx
 	addl	R(IdlePTD), %ebx
 	orl	$(PG_V|PG_RW|PG_PS), %eax

Modified: head/sys/i386/i386/pmap.c
==============================================================================
--- head/sys/i386/i386/pmap.c	Mon Dec 18 05:29:38 2017	(r326928)
+++ head/sys/i386/i386/pmap.c	Mon Dec 18 09:32:56 2017	(r326929)
@@ -662,7 +662,7 @@ pmap_set_pg(void)
 	endva = KERNBASE + KERNend;
 
 	if (pseflag) {
-		va = KERNBASE + KERNLOAD;
+		va = KERNBASE + roundup2(KERNLOAD, NBPDR);
 		while (va  < endva) {
 			pdir_pde(PTD, va) |= pgeflag;
 			invltlb();	/* Flush non-PG_G entries. */

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