linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Matt Redfearn <matt.redfearn@imgtec.com>
To: Ralf Baechle <ralf@linux-mips.org>
Cc: <linux-mips@linux-mips.org>,
	"Jason A . Donenfeld" <Jason@zx2c4.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Matt Redfearn <matt.redfearn@imgtec.com>,
	<linux-kernel@vger.kernel.org>,
	James Hogan <james.hogan@imgtec.com>,
	Paul Burton <paul.burton@imgtec.com>
Subject: [PATCH v3 3/5] MIPS: Only change $28 to thread_info if coming from user mode
Date: Mon, 19 Dec 2016 14:20:58 +0000	[thread overview]
Message-ID: <1482157260-18730-4-git-send-email-matt.redfearn@imgtec.com> (raw)
In-Reply-To: <1482157260-18730-1-git-send-email-matt.redfearn@imgtec.com>

The SAVE_SOME macro is used to save the execution context on all
exceptions.
If an exception occurs while executing user code, the stack is switched
to the kernel's stack for the current task, and register $28 is switched
to point to the current_thread_info, which is at the bottom of the stack
region.
If the exception occurs while executing kernel code, the stack is left,
and this change ensures that register $28 is not updated. This is the
correct behaviour when the kernel can be executing on the separate irq
stack, because the thread_info will not be at the base of it.

With this change, register $28 is only switched to it's kernel
conventional usage of the currrent thread info pointer at the point at
which execution enters kernel space. Doing it on every exception was
redundant, but OK without an IRQ stack, but will be erroneous once that
is introduced.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>

---

Changes in v3:
Drop superfluous nop that would have been in delay slot with .set
noreorder but is no longer required now that the code is .set reorder.

Changes in v2:
Drop .set reorder/noreorder when updating $28

 arch/mips/include/asm/stackframe.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h
index eebf39549606..2f182bdf024f 100644
--- a/arch/mips/include/asm/stackframe.h
+++ b/arch/mips/include/asm/stackframe.h
@@ -216,12 +216,19 @@
 		LONG_S	$25, PT_R25(sp)
 		LONG_S	$28, PT_R28(sp)
 		LONG_S	$31, PT_R31(sp)
+
+		/* Set thread_info if we're coming from user mode */
+		mfc0	k0, CP0_STATUS
+		sll	k0, 3		/* extract cu0 bit */
+		bltz	k0, 9f
+
 		ori	$28, sp, _THREAD_MASK
 		xori	$28, _THREAD_MASK
 #ifdef CONFIG_CPU_CAVIUM_OCTEON
 		.set    mips64
 		pref    0, 0($28)       /* Prefetch the current pointer */
 #endif
+9:
 		.set	pop
 		.endm
 
-- 
2.7.4

  parent reply	other threads:[~2016-12-19 14:21 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-19 14:20 [PATCH v3 0/5] MIPS: Add per-cpu IRQ stack Matt Redfearn
2016-12-19 14:20 ` [PATCH v3 1/5] MIPS: Introduce irq_stack Matt Redfearn
2016-12-19 14:20 ` [PATCH v3 2/5] MIPS: Stack unwinding while on IRQ stack Matt Redfearn
2016-12-19 14:20 ` Matt Redfearn [this message]
2016-12-21 12:13   ` [PATCH v3 3/5] MIPS: Only change $28 to thread_info if coming from user mode Maciej W. Rozycki
2016-12-19 14:20 ` [PATCH v3 4/5] MIPS: Switch to the irq_stack in interrupts Matt Redfearn
2016-12-19 14:21 ` [PATCH v3 5/5] MIPS: Select HAVE_IRQ_EXIT_ON_IRQ_STACK Matt Redfearn
2016-12-21  1:18 ` [PATCH v3 0/5] MIPS: Add per-cpu IRQ stack Jason A. Donenfeld
2017-01-10 23:32   ` Jason A. Donenfeld
2017-01-11  1:20     ` Ralf Baechle
2017-01-11 23:32       ` Jason A. Donenfeld
2017-01-13  9:49         ` James Hogan
2017-01-15 13:39           ` Jason A. Donenfeld
2017-01-15 13:48             ` Greg Kroah-Hartman
2017-01-15 14:11               ` Jason A. Donenfeld
2017-01-15 14:15                 ` Jason A. Donenfeld
2017-01-15 14:30                   ` Greg Kroah-Hartman
2017-01-15 18:07                     ` Jason A. Donenfeld

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=1482157260-18730-4-git-send-email-matt.redfearn@imgtec.com \
    --to=matt.redfearn@imgtec.com \
    --cc=Jason@zx2c4.com \
    --cc=james.hogan@imgtec.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mips@linux-mips.org \
    --cc=paul.burton@imgtec.com \
    --cc=ralf@linux-mips.org \
    --cc=tglx@linutronix.de \
    --subject='Re: [PATCH v3 3/5] MIPS: Only change $28 to thread_info if coming from user mode' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).