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

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Message-Id: <20170608073528.52b17428@mschwideX1>
Date:   Thu, 8 Jun 2017 07:35:28 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Heiko Carstens <heiko.carstens@...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, 7 Jun 2017 22:47:56 +0200
Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> 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...

Does it matter if it fails for a 32-bit ELF file? Just makes the code more
complex without benefit, no?

> > 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?

Yes, that makes it more consistent. I'll add it.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.