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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: 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>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [patch V2 08/16] x86/ioperm: Add bitmap sequence number
Date: Mon, 11 Nov 2019 23:03:22 +0100
Message-ID: <20191111223052.292300453@linutronix.de> (raw)
In-Reply-To: <20191111220314.519933535@linutronix.de>

Add a globally unique sequence number which is incremented when ioperm() is
changing the I/O bitmap of a task. Store the new sequence number in the
io_bitmap structure and compare it along with the actual struct pointer
with the one which was last loaded on a CPU. Only update the bitmap if
either of the two changes. That should further reduce the overhead of I/O
bitmap scheduling when there are only a few I/O bitmap users on the system.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch
---
 arch/x86/include/asm/iobitmap.h  |    1 
 arch/x86/include/asm/processor.h |    8 +++++++
 arch/x86/kernel/cpu/common.c     |    1 
 arch/x86/kernel/ioport.c         |    9 +++++---
 arch/x86/kernel/process.c        |   40 +++++++++++++++++++++++++++++----------
 5 files changed, 46 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/iobitmap.h
+++ b/arch/x86/include/asm/iobitmap.h
@@ -5,6 +5,7 @@
 #include <asm/processor.h>
 
 struct io_bitmap {
+	u64			sequence;
 	unsigned int		io_bitmap_max;
 	union {
 		unsigned long	bits[IO_BITMAP_LONGS];
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -366,6 +366,14 @@ struct tss_struct {
 	struct x86_hw_tss	x86_tss;
 
 	/*
+	 * The bitmap pointer and the sequence number of the last active
+	 * bitmap. last_bitmap cannot be dereferenced. It's solely for
+	 * comparison.
+	 */
+	struct io_bitmap	*last_bitmap;
+	u64			last_sequence;
+
+	/*
 	 * Store the dirty size of the last io bitmap offender. The next
 	 * one will have to do the cleanup as the switch out to a non io
 	 * bitmap user will just set x86_tss.io_bitmap_base to a value
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1861,6 +1861,7 @@ void cpu_init(void)
 	/* Initialize the TSS. */
 	tss_setup_ist(tss);
 	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+	tss->last_bitmap = NULL;
 	tss->io_bitmap_prev_max = 0;
 	memset(tss->io_bitmap_bytes, 0xff, sizeof(tss->io_bitmap_bytes));
 	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -14,6 +14,8 @@
 #include <asm/iobitmap.h>
 #include <asm/desc.h>
 
+static atomic64_t io_bitmap_sequence;
+
 /*
  * this changes the io permissions bitmap in the current task.
  */
@@ -76,14 +78,15 @@ long ksys_ioperm(unsigned long from, uns
 
 	iobm->io_bitmap_max = bytes;
 
-	/* Update the TSS: */
-	memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, bytes_updated);
-
+	/* Update the sequence number to force an update in switch_to() */
+	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
 	/* Set the tasks io_bitmap pointer (might be the same) */
 	t->io_bitmap = iobm;
 	/* Mark it active for context switching */
 	set_thread_flag(TIF_IO_BITMAP);
 
+	/* Update the TSS: */
+	memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, bytes_updated);
 	/* Make the bitmap base in the TSS valid */
 	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
 
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -354,6 +354,29 @@ void arch_setup_new_exec(void)
 	}
 }
 
+static void switch_to_update_io_bitmap(struct tss_struct *tss,
+				       struct io_bitmap *iobm)
+{
+	/*
+	 * Copy at least the byte range of the incoming tasks bitmap which
+	 * covers the permitted I/O ports.
+	 *
+	 * If the previous task which used an I/O bitmap had more bits
+	 * permitted, then the copy needs to cover those as well so they
+	 * get turned off.
+	 */
+	memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes,
+	       max(tss->io_bitmap_prev_max, iobm->io_bitmap_max));
+
+	/*
+	 * Store the new max and the sequence number of this bitmap
+	 * and a pointer to the bitmap itself.
+	 */
+	tss->io_bitmap_prev_max = iobm->io_bitmap_max;
+	tss->last_sequence = iobm->sequence;
+	tss->last_bitmap = iobm;
+}
+
 static inline void switch_to_bitmap(struct thread_struct *next,
 				    unsigned long tifp, unsigned long tifn)
 {
@@ -363,18 +386,15 @@ static inline void switch_to_bitmap(stru
 		struct io_bitmap *iobm = next->io_bitmap;
 
 		/*
-		 * Copy at least the size of the incoming tasks bitmap
-		 * which covers the last permitted I/O port.
-		 *
-		 * If the previous task which used an io bitmap had more
-		 * bits permitted, then the copy needs to cover those as
-		 * well so they get turned off.
+		 * Only copy bitmap data when the bitmap or the sequence
+		 * number differs. The update time is accounted to the
+		 * incoming task.
 		 */
-		memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes,
-		       max(tss->io_bitmap_prev_max, iobm->io_bitmap_max));
+		if (tss->last_bitmap != iobm ||
+		    tss->last_sequence != iobm->sequence)
+			switch_to_update_io_bitmap(tss, iobm);
 
-		/* Store the new max and set io_bitmap_base valid */
-		tss->io_bitmap_prev_max = iobm->io_bitmap_max;
+		/* Enable the bitmap */
 		tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
 
 		/*



  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 ` Thomas Gleixner [this message]
2019-11-12  9:22   ` [patch V2 08/16] x86/ioperm: Add bitmap sequence number 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   ` [PATCH] x86/iopl: Clear up the role of the two bitmap copying fields Ingo Molnar
2019-11-12  8:15   ` [PATCH] x86/iopl: Rename <asm/iobitmap.h> to <asm/io_bitmap.h> Ingo Molnar

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