LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Linus Torvalds <torvalds@linuxfoundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Willy Tarreau <w@1wt.eu>, Juergen Gross <jgross@suse.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH] x86/iopl: Clear up the role of the two bitmap copying fields
Date: Tue, 12 Nov 2019 09:11:53 +0100
Message-ID: <20191112081153.GG100264@gmail.com> (raw)
In-Reply-To: <20191112074052.GD100264@gmail.com>


Here's another one, which makes the pointer-caching logic a bit clearer 
IMO:

Firstly, it lines up the two related fields in the namespace:

   x86_io_bitmap.last_bitmap        =>   bitmap_copied_ptr
   x86_io_bitmap.last_sequence      =>   bitmap_copied_seq

It also constifies the pointer to better signal that it should never 
actually be used for anything but comparison

I think the 'bitmap_copied_' ptr/seq pairing makes it more obvious, and 
removing the 'last' language makes it a tiny bit clearer that this bitmap 
is special because we copied its contents into the TSS.

This makes code like this a tiny bit easier to read IMHO:

+                       if (tss->io_bitmap.bitmap_copied_ptr != iobm ||
+                           tss->io_bitmap.bitmap_copied_seq != iobm->sequence)

I marked it RFC because you might not agree. :-)

Only build tested.

Thanks,

	Ingo

---
 arch/x86/include/asm/processor.h | 10 +++++-----
 arch/x86/kernel/cpu/common.c     |  2 +-
 arch/x86/kernel/process.c        |  8 ++++----
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d1f2c1eb14e9..b45ff7c1419f 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -367,12 +367,12 @@ struct entry_stack_page {
 struct x86_io_bitmap
 {
 	/*
-	 * The bitmap pointer and the sequence number of the last active
-	 * bitmap. last_bitmap cannot be dereferenced. It's solely for
-	 * comparison.
+	 * The bitmap pointer and the sequence number of the last copied
+	 * bitmap. bitmap_copied_ptr must not be dereferenced, it's solely
+	 * for comparison.
 	 */
-	struct io_bitmap	*last_bitmap;
-	u64			last_sequence;
+	const struct io_bitmap	*bitmap_copied_ptr;
+	u64			bitmap_copied_seq;
 
 	/*
 	 * Store the dirty size of the last io bitmap offender. The next
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a35a557429e7..5a74c5b11b1c 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1861,7 +1861,7 @@ void cpu_init(void)
 	/* Initialize the TSS. */
 	tss_setup_ist(tss);
 	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
-	tss->io_bitmap.last_bitmap = NULL;
+	tss->io_bitmap.bitmap_copied_ptr = NULL;
 	tss->io_bitmap.bytes_max = 0;
 	memset(tss->io_bitmap.map_bytes, 0xff, sizeof(tss->io_bitmap.map_bytes));
 	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c4e76a540b51..ecf97855ed68 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -358,8 +358,8 @@ static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm)
 	 * and a pointer to the bitmap itself.
 	 */
 	tss->io_bitmap.bytes_max = iobm->bytes_max;
-	tss->io_bitmap.last_sequence = iobm->sequence;
-	tss->io_bitmap.last_bitmap = iobm;
+	tss->io_bitmap.bitmap_copied_seq = iobm->sequence;
+	tss->io_bitmap.bitmap_copied_ptr = iobm;
 }
 
 /**
@@ -388,8 +388,8 @@ void tss_update_io_bitmap(void)
 			 * sequence number differs. The update time is
 			 * accounted to the incoming task.
 			 */
-			if (tss->io_bitmap.last_bitmap != iobm ||
-			    tss->io_bitmap.last_sequence != iobm->sequence)
+			if (tss->io_bitmap.bitmap_copied_ptr != iobm ||
+			    tss->io_bitmap.bitmap_copied_seq != iobm->sequence)
 				tss_copy_io_bitmap(tss, iobm);
 
 			/* Enable the bitmap */

  parent reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-11 22:03 [patch V2 00/16] x86/iopl: Prevent user space from using CLI/STI with iopl(3) Thomas Gleixner
2019-11-11 22:03 ` [patch V2 01/16] x86/ptrace: Prevent truncation of bitmap size Thomas Gleixner
2019-11-12 15:34   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 02/16] x86/process: Unify copy_thread_tls() Thomas Gleixner
2019-11-11 22:03 ` [patch V2 03/16] x86/cpu: Unify cpu_init() Thomas Gleixner
2019-11-11 22:03 ` [patch V2 04/16] x86/tss: Fix and move VMX BUILD_BUG_ON() Thomas Gleixner
2019-11-11 22:44   ` Paolo Bonzini
2019-11-12 15:37   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 05/16] x86/iopl: Cleanup include maze Thomas Gleixner
2019-11-12 15:37   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 06/16] x86/io: Speedup schedule out of I/O bitmap user Thomas Gleixner
2019-11-12 16:00   ` Andy Lutomirski
2019-11-12 17:08     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 07/16] x86/ioperm: Move iobitmap data into a struct Thomas Gleixner
2019-11-12 16:02   ` Andy Lutomirski
2019-11-12 17:08     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 08/16] x86/ioperm: Add bitmap sequence number Thomas Gleixner
2019-11-12  9:22   ` Peter Zijlstra
2019-11-12  9:55     ` [patch V2 08/16] x86/ioperm: Add bitmap sequence numberc Thomas Gleixner
2019-11-12 16:08   ` [patch V2 08/16] x86/ioperm: Add bitmap sequence number Andy Lutomirski
2019-11-12 17:10     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 09/16] x86/ioperm: Move TSS bitmap update to exit to user work Thomas Gleixner
2019-11-12 16:16   ` Andy Lutomirski
2019-11-12 17:20     ` Thomas Gleixner
2019-11-12 17:41       ` Andy Lutomirski
2019-11-12 17:46         ` Linus Torvalds
2019-11-13  8:30           ` Peter Zijlstra
2019-11-11 22:03 ` [patch V2 10/16] x86/ioperm: Remove bitmap if all permissions dropped Thomas Gleixner
2019-11-12 17:43   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 11/16] x86/ioperm: Share I/O bitmap if identical Thomas Gleixner
2019-11-12  7:14   ` Ingo Molnar
2019-11-12  7:17     ` Thomas Gleixner
2019-11-12  7:52       ` Ingo Molnar
2019-11-12  9:15   ` Peter Zijlstra
2019-11-12  9:51     ` Thomas Gleixner
2019-11-14 11:02     ` David Laight
2019-11-14 12:39       ` Thomas Gleixner
2019-11-14 13:09       ` Peter Zijlstra
2019-11-14 13:22         ` David Laight
2019-11-12 18:12   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 12/16] selftests/x86/ioperm: Extend testing so the shared bitmap is exercised Thomas Gleixner
2019-11-11 22:03 ` [patch V2 13/16] x86/iopl: Fixup misleading comment Thomas Gleixner
2019-11-12 18:14   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 14/16] x86/iopl: Restrict iopl() permission scope Thomas Gleixner
2019-11-11 23:03   ` Thomas Gleixner
2019-11-12  6:32     ` Ingo Molnar
2019-11-12  8:42   ` Ingo Molnar
2019-11-12 10:07     ` Thomas Gleixner
2019-11-12 18:35   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 15/16] x86/iopl: Remove legacy IOPL option Thomas Gleixner
2019-11-12 18:37   ` Andy Lutomirski
2019-11-12 19:40     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 16/16] selftests/x86/iopl: Extend test to cover IOPL emulation Thomas Gleixner
2019-11-12  7:40 ` [PATCH] x86/iopl: Factor out IO-bitmap related TSS fields into 'struct x86_io_bitmap' Ingo Molnar
2019-11-12  7:59   ` [PATCH] x86/iopl: Harmonize 'struct io_bitmap' and 'struct x86_io_bitmap' nomenclature Ingo Molnar
2019-11-12  8:11   ` Ingo Molnar [this message]
2019-11-12  8:15   ` [PATCH] x86/iopl: Rename <asm/iobitmap.h> to <asm/io_bitmap.h> Ingo Molnar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191112081153.GG100264@gmail.com \
    --to=mingo@kernel.org \
    --cc=hpa@zytor.com \
    --cc=jgross@suse.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=sean.j.christopherson@intel.com \
    --cc=stephen@networkplumber.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linuxfoundation.org \
    --cc=w@1wt.eu \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git