[PATCH 0/2] x86/boot: Further reserve_boot_regions() cleanups

[PATCH 0/2] x86/boot: Further reserve_boot_regions() cleanups

[Andy Lutomirski]

This follows up on Ingo's cleanup.  The first patch fixes the docs
and the second makes the code even more comprehensible.

Andy Lutomirski (2):
  x86/boot: Clarify what x86_legacy_features.reserve_bios_regions does
  x86/boot: Simplify EBDA-vs-BIOS reservation logic

 arch/x86/include/asm/x86_init.h |  5 +++--
 arch/x86/kernel/ebda.c          | 34 +++++++++++-----------------------
 2 files changed, 14 insertions(+), 25 deletions(-)

-- 
2.7.4

[PATCH 1/2] x86/boot: Clarify what x86_legacy_features.reserve_bios_regions does

[Andy Lutomirski]

It doesn't just control probing for the EBDA -- it controls whether we
detect and reserve the <1MB BIOS regions in general.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/x86_init.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index c519c052700a..66c15a01667f 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -168,8 +168,9 @@ struct x86_legacy_devices {
  * struct x86_legacy_features - legacy x86 features
  *
  * @rtc: this device has a CMOS real-time clock present
- * @reserve_bios_regions: it's safe to search for the EBDA signature in the hardware's
- * 	low RAM
+ * @reserve_bios_regions: boot code will search for the EBDA address and the
+ * 	start of the 640k - 1M BIOS region.  If false, the platform must
+ * 	ensure that its memory map correctly reserves sub-1MB regions as needed.
  * @devices: legacy x86 devices, refer to struct x86_legacy_devices
  * 	documentation for further details.
  */
-- 
2.7.4

[PATCH 2/2] x86/boot: Simplify EBDA-vs-BIOS reservation logic

[Andy Lutomirski]

Both the intent and the effect of reserve_bios_regions() is simple:
reserve the range from the apparent BIOS start (suitably filtered)
through 1MB and, if the EBDA start address is sensible, extend that
reservation downward to cover the EBDA as well.

The code is overcomplicated, though, and contains head-scratchers
like:

	if (ebda_start < BIOS_START_MIN)
		ebda_start = BIOS_START_MAX;

That snipped is trying to say "if ebda_start < BIOS_START_MIN,
ignore it".

Simplify it: reorder the code so that it makes sense.  This should
have no functional effect under any circumstances.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/kernel/ebda.c | 34 +++++++++++-----------------------
 1 file changed, 11 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/ebda.c b/arch/x86/kernel/ebda.c
index 6219eef20e2e..4312f8ae71b7 100644
--- a/arch/x86/kernel/ebda.c
+++ b/arch/x86/kernel/ebda.c
@@ -65,22 +65,6 @@ void __init reserve_bios_regions(void)
 	if (!x86_platform.legacy.reserve_bios_regions)
 		return;
 
-	/* Get the start address of the EBDA page: */
-	ebda_start = get_bios_ebda();
-
-	/*
-	 * Quirk: some old Dells seem to have a 4k EBDA without
-	 * reporting so in their BIOS RAM size value, so just
-	 * consider the memory above 640K to be off limits
-	 * (bugzilla 2990).
-	 *
-	 * We detect this case by filtering for nonsensical EBDA
-	 * addresses below 128K, where we can assume that they
-	 * are bogus and bump it up to a fixed 640K value:
-	 */
-	if (ebda_start < BIOS_START_MIN)
-		ebda_start = BIOS_START_MAX;
-
 	/*
 	 * BIOS RAM size is encoded in kilobytes, convert it
 	 * to bytes to get a first guess at where the BIOS
@@ -91,18 +75,22 @@ void __init reserve_bios_regions(void)
 
 	/*
 	 * If bios_start is less than 128K, assume it is bogus
-	 * and bump it up to 640K:
+	 * and bump it up to 640K.  Similarly, if bios_start is above 640K,
+	 * don't trust it.
 	 */
-	if (bios_start < BIOS_START_MIN)
+	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
 		bios_start = BIOS_START_MAX;
 
+	/* Get the start address of the EBDA page: */
+	ebda_start = get_bios_ebda();
+
 	/*
-	 * Use the lower of the bios_start and ebda_start
-	 * as the starting point, but don't allow it to
-	 * go beyond 640K:
+	 * If the EBDA start address is sane and is below the BIOS region,
+	 * then also reserve everything from the EBDA start address up to
+	 * the BIOS region.
 	 */
-	bios_start = min(bios_start, ebda_start);
-	bios_start = min(bios_start, BIOS_START_MAX);
+	if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)
+		bios_start = ebda_start;
 
 	/* Reserve all memory between bios_start and the 1MB mark: */
 	memblock_reserve(bios_start, 0x100000 - bios_start);
-- 
2.7.4

[tip:x86/boot] x86/boot: Clarify what x86_legacy_features.reserve_bios_regions does

[tip-bot for Andy Lutomirski]

Commit-ID:  30f027398b329c75c8f23a3c13be240b50866fdc
Gitweb:     http://git.kernel.org/tip/30f027398b329c75c8f23a3c13be240b50866fdc
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Thu, 21 Jul 2016 14:16:51 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 22 Jul 2016 11:46:01 +0200

x86/boot: Clarify what x86_legacy_features.reserve_bios_regions does

It doesn't just control probing for the EBDA -- it controls whether we
detect and reserve the <1MB BIOS regions in general.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Mario Limonciello <mario_limonciello@dell.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Link: http://lkml.kernel.org/r/55bd591115498440d461857a7b64f349a5d911f3.1469135598.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/x86_init.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index c519c05..66c15a0 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -168,8 +168,9 @@ struct x86_legacy_devices {
  * struct x86_legacy_features - legacy x86 features
  *
  * @rtc: this device has a CMOS real-time clock present
- * @reserve_bios_regions: it's safe to search for the EBDA signature in the hardware's
- * 	low RAM
+ * @reserve_bios_regions: boot code will search for the EBDA address and the
+ * 	start of the 640k - 1M BIOS region.  If false, the platform must
+ * 	ensure that its memory map correctly reserves sub-1MB regions as needed.
  * @devices: legacy x86 devices, refer to struct x86_legacy_devices
  * 	documentation for further details.
  */

[tip:x86/boot] x86/boot: Simplify EBDA-vs-BIOS reservation logic

[tip-bot for Andy Lutomirski]

Commit-ID:  6a79296cb15d947bcb4558011fe066e5d8252b35
Gitweb:     http://git.kernel.org/tip/6a79296cb15d947bcb4558011fe066e5d8252b35
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Thu, 21 Jul 2016 14:16:52 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 22 Jul 2016 11:46:01 +0200

x86/boot: Simplify EBDA-vs-BIOS reservation logic

Both the intent and the effect of reserve_bios_regions() is simple:
reserve the range from the apparent BIOS start (suitably filtered)
through 1MB and, if the EBDA start address is sensible, extend that
reservation downward to cover the EBDA as well.

The code is overcomplicated, though, and contains head-scratchers
like:

	if (ebda_start < BIOS_START_MIN)
		ebda_start = BIOS_START_MAX;

That snipped is trying to say "if ebda_start < BIOS_START_MIN,
ignore it".

Simplify it: reorder the code so that it makes sense.  This should
have no functional effect under any circumstances.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Mario Limonciello <mario_limonciello@dell.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Link: http://lkml.kernel.org/r/ef89c0c761be20ead8bd9a3275743e6259b6092a.1469135598.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/ebda.c | 34 +++++++++++-----------------------
 1 file changed, 11 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/ebda.c b/arch/x86/kernel/ebda.c
index 6219eef..4312f8a 100644
--- a/arch/x86/kernel/ebda.c
+++ b/arch/x86/kernel/ebda.c
@@ -65,22 +65,6 @@ void __init reserve_bios_regions(void)
 	if (!x86_platform.legacy.reserve_bios_regions)
 		return;
 
-	/* Get the start address of the EBDA page: */
-	ebda_start = get_bios_ebda();
-
-	/*
-	 * Quirk: some old Dells seem to have a 4k EBDA without
-	 * reporting so in their BIOS RAM size value, so just
-	 * consider the memory above 640K to be off limits
-	 * (bugzilla 2990).
-	 *
-	 * We detect this case by filtering for nonsensical EBDA
-	 * addresses below 128K, where we can assume that they
-	 * are bogus and bump it up to a fixed 640K value:
-	 */
-	if (ebda_start < BIOS_START_MIN)
-		ebda_start = BIOS_START_MAX;
-
 	/*
 	 * BIOS RAM size is encoded in kilobytes, convert it
 	 * to bytes to get a first guess at where the BIOS
@@ -91,18 +75,22 @@ void __init reserve_bios_regions(void)
 
 	/*
 	 * If bios_start is less than 128K, assume it is bogus
-	 * and bump it up to 640K:
+	 * and bump it up to 640K.  Similarly, if bios_start is above 640K,
+	 * don't trust it.
 	 */
-	if (bios_start < BIOS_START_MIN)
+	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
 		bios_start = BIOS_START_MAX;
 
+	/* Get the start address of the EBDA page: */
+	ebda_start = get_bios_ebda();
+
 	/*
-	 * Use the lower of the bios_start and ebda_start
-	 * as the starting point, but don't allow it to
-	 * go beyond 640K:
+	 * If the EBDA start address is sane and is below the BIOS region,
+	 * then also reserve everything from the EBDA start address up to
+	 * the BIOS region.
 	 */
-	bios_start = min(bios_start, ebda_start);
-	bios_start = min(bios_start, BIOS_START_MAX);
+	if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)
+		bios_start = ebda_start;
 
 	/* Reserve all memory between bios_start and the 1MB mark: */
 	memblock_reserve(bios_start, 0x100000 - bios_start);