linux-kernel - [tip: x86/iopl] x86/ioperm: Avoid bitmap allocation if no permissions are set

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Date:   Fri, 15 Nov 2019 21:12:30 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/iopl] x86/ioperm: Avoid bitmap allocation if no permissions are set

The following commit has been merged into the x86/iopl branch of tip:

Commit-ID:     5487da6bf0775d996352442b89a8defbd671b4ae
Gitweb:        https://git.kernel.org/tip/5487da6bf0775d996352442b89a8defbd671b4ae
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 13 Nov 2019 21:42:47 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 14 Nov 2019 20:15:02 +01:00

x86/ioperm: Avoid bitmap allocation if no permissions are set

If ioperm() is invoked the first time and the @turn_on argument is 0, then
there is no point to allocate a bitmap just to clear permissions which are
not set.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20191113210104.404509322@linutronix.de

---
 arch/x86/kernel/ioport.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index ca6aa1e..80fa36b 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -36,6 +36,9 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 	 */
 	bitmap = t->io_bitmap_ptr;
 	if (!bitmap) {
+		/* No point to allocate a bitmap just to clear permissions */
+		if (!turn_on)
+			return 0;
 		bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
 		if (!bitmap)
 			return -ENOMEM;