Re: [PATCH v2 1/2] altp2m: Merge p2m_set_altp2m_mem_access and p2m_set_mem_access

["Jan Beulich" <JBeulich@suse.com>]

>>> On 28.01.16 at 21:58, <tlengyel@novetta.com> wrote:
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1777,14 +1777,57 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long gla,
>      return (p2ma == p2m_access_n2rwx);
>  }
>  
> +static int p2m_set_altp2m_mem_access(struct domain *d, struct p2m_domain *hp2m,
> +                                     struct p2m_domain *ap2m, p2m_access_t a,
> +                                     unsigned long gfn)

I think new functions would better not use "unsigned long" for frame
numbers.

> +{
> +    mfn_t mfn;
> +    p2m_type_t t;
> +    p2m_access_t old_a;
> +    unsigned int page_order;
> +    int rc;
> +
> +    mfn = ap2m->get_entry(ap2m, gfn, &t, &old_a, 0, NULL, NULL);
> +
> +    /* Check host p2m if no valid entry in alternate */
> +    if ( !mfn_valid(mfn) )
> +    {
> +        mfn = hp2m->get_entry(hp2m, gfn, &t, &old_a,
> +                              P2M_ALLOC | P2M_UNSHARE, &page_order, NULL);
> +
> +        rc = -ESRCH;
> +        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
> +            goto out;
> +
> +        /* If this is a superpage, copy that first */
> +        if ( page_order != PAGE_ORDER_4K )
> +        {
> +            unsigned long mask = ~((1UL << page_order) - 1);
> +            gfn_t gfn2 = _gfn(gfn & mask);
> +            mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
> +
> +            rc = ap2m->set_entry(ap2m, gfn_x(gfn2), mfn2, page_order, t, old_a, 1);
> +            if ( rc )
> +                goto out;
> +        }
> +    }
> +
> +    rc = ap2m->set_entry(ap2m, gfn, mfn, PAGE_ORDER_4K, t, a,
> +                         (current->domain != d));
> +
> + out:
> +    return rc;
> +}

With there not being any involved error handling here, I don't think
using a label and goto is warranted here. But I'll leave the ultimate
decision to George, of course.

> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -423,11 +423,14 @@ struct xen_mem_access_op {
>      /* xenmem_access_t */
>      uint8_t access;
>      domid_t domid;
> +    uint16_t altp2m_idx;
> +    uint16_t _pad;
>      /*
>       * Number of pages for set op
>       * Ignored on setting default access and other ops
>       */
>      uint32_t nr;
> +    uint32_t _pad2;

Repeating what I had said on v1: So this is a tools only interface,
yes. But it's not versioned (other than e.g. domctl and sysctl), so
altering the interface structure is at least fragile.

Jan