This is a note to let you know that I've just added the patch titled

s390: fix alloc_pgste check in init_new_context again

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: s390-fix-alloc_pgste-check-in-init_new_context-again.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Thu Feb 1 13:45:42 CET 2018

From: Martin Schwidefsky schwidefsky@de.ibm.com Date: Wed, 22 Nov 2017 17:19:32 +0100 Subject: s390: fix alloc_pgste check in init_new_context again

From: Martin Schwidefsky schwidefsky@de.ibm.com

[ Upstream commit 53c4ab70c11c3ba1b9e3caa8e8c17e9c16d9cbc0 ]

git commit badb8bb983e9 "fix alloc_pgste check in init_new_context" fixed the problem of 'current->mm == NULL' in init_new_context back in 2011.

git commit 3eabaee998c7 "KVM: s390: allow sie enablement for multi- threaded programs" completely removed the check against alloc_pgste.

git commit 23fefe119ceb "s390/kvm: avoid global config of vm.alloc_pgste=1" re-added a check against the alloc_pgste flag but without the required check for current->mm != NULL.

For execve() called by a kernel thread init_new_context() reads from ((struct mm_struct *) NULL)->context.alloc_pgste to decide between 2K vs 4K page tables. If the bit happens to be set for the init process it will be created with large page tables. This decision is inherited by all the children of init, this waste quite some memory.

Re-add the check for 'current->mm != NULL'.

Fixes: 23fefe119ceb ("s390/kvm: avoid global config of vm.alloc_pgste=1") Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/s390/include/asm/mmu_context.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -28,7 +28,7 @@ static inline int init_new_context(struc #ifdef CONFIG_PGSTE mm->context.alloc_pgste = page_table_allocate_pgste || test_thread_flag(TIF_PGSTE) || - current->mm->context.alloc_pgste; + (current->mm && current->mm->context.alloc_pgste); mm->context.has_pgste = 0; mm->context.use_skey = 0; mm->context.use_cmma = 0;

Patches currently in stable-queue which might be from schwidefsky@de.ibm.com are

queue-4.14/s390-zcrypt-fix-wrong-comparison-leading-to-strange-load-balancing.patch queue-4.14/s390-fix-alloc_pgste-check-in-init_new_context-again.patch queue-4.14/s390-topology-fix-compile-error-in-file-arch-s390-kernel-smp.c.patch