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

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Date:	Fri, 28 Feb 2014 12:52:18 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org
CC:	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...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: Re: [PATCH 2/4] mm, s390: Ignore MADV_HUGEPAGE on s390 to prevent
 SIGSEGV in qemu

On 27/02/14 18:23, Alex Thorlton wrote:
> 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!
>  		 */
> 


Tested-by: Christian Borntraeger <borntraeger@...ibm.com>

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