[tip:x86/pti] perf/core: Make sure the ring-buffer is mapped in all page-tables

[tip-bot for Joerg Roedel]

Commit-ID:  77754cfa09a6c528c38cbca9ee4cc4f7cf6ad6f2
Gitweb:     https://git.kernel.org/tip/77754cfa09a6c528c38cbca9ee4cc4f7cf6ad6f2
Author:     Joerg Roedel <jroedel@xxxxxxx>
AuthorDate: Fri, 20 Jul 2018 18:22:22 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 20 Jul 2018 22:33:41 +0200

perf/core: Make sure the ring-buffer is mapped in all page-tables

The ring-buffer is accessed in the NMI handler, so it's better to avoid
faulting on it. Sync the vmalloc range with all page-tables in system to
make sure everyone has it mapped.

This fixes a WARN_ON_ONCE() that can be triggered with PTI enabled on
x86-32:

  WARNING: CPU: 4 PID: 0 at arch/x86/mm/fault.c:320 vmalloc_fault+0x220/0x230

This triggers because with PTI enabled on an PAE kernel the PMDs are no
longer shared between the page-tables, so the vmalloc changes do not
propagate automatically.

Note: Andy said rightfully that we should try to fix the vmalloc code for
that case, but that's not a hot fix for the issue at hand.

Fixes: 7757d607c6b3 ("x86/pti: Allow CONFIG_PAGE_TABLE_ISOLATION for x86_32")
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Eduardo Valentin <eduval@xxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: aliguori@xxxxxxxxxx
Cc: daniel.gruss@xxxxxxxxxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: keescook@xxxxxxxxxx
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Waiman Long <llong@xxxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: "David H . Gutteridge" <dhgutteridge@xxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: joro@xxxxxxxxxx
Link: https://lkml.kernel.org/r/1532103744-31902-2-git-send-email-joro@xxxxxxxxxx

---
 kernel/events/ring_buffer.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 5d3cf407e374..df2d8cf0072c 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -814,6 +814,13 @@ static void rb_free_work(struct work_struct *work)
 
 	vfree(base);
 	kfree(rb);
+
+	/*
+	 * FIXME: PAE workaround for vmalloc_fault(): Make sure buffer is
+	 * unmapped in all page-tables.
+	 */
+	if (IS_ENABLED(CONFIG_X86_PAE))
+		vmalloc_sync_all();
 }
 
 void rb_free(struct ring_buffer *rb)
@@ -840,6 +847,15 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 	if (!all_buf)
 		goto fail_all_buf;
 
+	/*
+	 * FIXME: PAE workaround for vmalloc_fault(): The buffer is
+	 * accessed in NMI handlers, make sure it is mapped in all
+	 * page-tables in the system so that we don't fault on the range in
+	 * an NMI handler.
+	 */
+	if (IS_ENABLED(CONFIG_X86_PAE))
+		vmalloc_sync_all();
+
 	rb->user_page = all_buf;
 	rb->data_pages[0] = all_buf + PAGE_SIZE;
 	if (nr_pages) {