linux-kernel - [PATCH 2/4] mm, s390: Ignore MADV_HUGEPAGE on s390 to prevent SIGSEGV in qemu

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Date:	Thu, 27 Feb 2014 11:23:24 -0600
From:	Alex Thorlton <athorlton@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Alex Thorlton <athorlton@....com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>, linux390@...ibm.com,
	linux-s390@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org
Subject: [PATCH 2/4] mm, s390: Ignore MADV_HUGEPAGE on s390 to prevent SIGSEGV in qemu

As Christian pointed out, the recent 'Revert "thp: make MADV_HUGEPAGE
check for mm->def_flags"' breaks qemu, it does QEMU_MADV_HUGEPAGE for
all kvm pages but this doesn't work after s390_enable_sie/thp_split_mm.

Paolo suggested that instead of failing on the call to madvise, we
simply ignore the call (return 0).

Reported-by: Christian Borntraeger <borntraeger@...ibm.com>
Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Suggested-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Alex Thorlton <athorlton@....com>
Cc: Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Rik van Riel <riel@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: linux390@...ibm.com
Cc: linux-s390@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: linux-api@...r.kernel.org

---
 mm/huge_memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a4310a5..61d234d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1970,6 +1970,15 @@ int hugepage_madvise(struct vm_area_struct *vma,
 {
 	switch (advice) {
 	case MADV_HUGEPAGE:
+#ifdef CONFIG_S390
+		/*
+		 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
+		 * can't handle this properly after s390_enable_sie, so we simply
+		 * ignore the madvise to prevent qemu from causing a SIGSEGV.
+		 */
+		if (mm_has_pgste(vma->vm_mm))
+			return 0;
+#endif
 		/*
 		 * Be somewhat over-protective like KSM for now!
 		 */
-- 
1.7.12.4

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