linux-kernel - Re: [PATCH RFC 0/2] KVM: s390: avoid having to enable vm.alloc

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Date:   Wed, 7 Jun 2017 22:47:56 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Huth <thuth@...hat.com>,
        Andreas Krebbel <krebbel@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC 0/2] KVM: s390: avoid having to enable vm.alloc_pgste

On Wed, Jun 07, 2017 at 02:34:40PM +0200, Martin Schwidefsky wrote:
> +#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state)	\
> +({								\
> +	struct elf64_hdr *_ehdr = (void *) ehdr;		\
> +	struct elf64_phdr *_phdr = (void *) phdr;		\
> +	int _rc = 0;						\
> +	if (_ehdr->e_ident[EI_CLASS] == ELFCLASS64 &&		\
> +	    _phdr->p_type == PT_S390_REQUEST_PGSTE &&		\
> +	    !page_table_allocate_pgste &&			\
> +	    !test_thread_flag(TIF_REQUEST_PGSTE)) {		\
> +		set_thread_flag(TIF_REQUEST_PGSTE);		\
> +		set_pt_regs_flag(task_pt_regs(current),		\
> +				 PIF_SYSCALL_RESTART);		\
> +		_rc = -EAGAIN;					\
> +	}							\
> +	_rc;							\
> +})

I'm wondering if this should simply fail, if a PT_S390_REQUEST_PGSTE type
segment exists, but it is not ELFCLASS64?
It will fail later anyway on s390_enable_sie(), but...

> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
> index c119d564d8f2..1201b18e817d 100644
> --- a/arch/s390/include/asm/mmu_context.h
> +++ b/arch/s390/include/asm/mmu_context.h
> @@ -25,7 +25,8 @@ static inline int init_new_context(struct task_struct *tsk,
>  	mm->context.gmap_asce = 0;
>  	mm->context.flush_mm = 0;
>  #ifdef CONFIG_PGSTE
> -	mm->context.alloc_pgste = page_table_allocate_pgste;
> +	mm->context.alloc_pgste = page_table_allocate_pgste ||
> +		test_thread_flag(TIF_REQUEST_PGSTE);

I think the alloc_pgste flag should be inherited on fork, no?