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

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Date:   Fri, 2 Jun 2017 12:28:48 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Huth <thuth@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH RFC 0/2] KVM: s390: avoid having to enable vm.alloc_pgste

On Fri, Jun 02, 2017 at 11:46:47AM +0200, Martin Schwidefsky wrote:
> On Fri, 2 Jun 2017 09:02:10 +0200
> Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> > Maybe this is a bit over-simplified, but might work.
> This is not over-simplified at all, that does work:

Good!

> +struct arch_elf_state {
> +};
> +
> +#define INIT_ARCH_ELF_STATE { }
> +
> +#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) (0)
> +#define arch_check_elf(ehdr, interp, interp_ehdr, state)	\
> +({								\
> +	struct elf64_hdr *hdr = (void*) ehdr;			\
> +	int _rc = 0;						\
> +	if (hdr->e_ident[EI_CLASS] == ELFCLASS64 &&		\
> +	    (hdr->e_flags & 0x00000002) &&			\
> +	    !page_table_allocate_pgste &&			\
> +	    !current->mm->context.alloc_pgste) {		\
> +		current->mm->context.alloc_pgste = 1;		\

However, I think this is over-simplified, unless I'm mistaken.

If you set current->mm->context.alloc_pgste here, then that means that 4k
page tables will be freed when the original mm will be released, instead of
the correct 2k ones.

I think you need an additional intermediate context flag here. Something
like current->mm->context.request_pgste or whatever, no?