Re: [Xen-devel] [PATCH] iommu / p2m: add a page_order parameter to iommu_map/unmap_page()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/10/18 09:19, Paul Durrant wrote:
> diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
> index 55df18501e..b264a97bd8 100644
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -683,41 +684,13 @@ p2m_pt_set_entry(struct p2m_domain *p2m, gfn_t gfn_, 
> mfn_t mfn,
>      {
>          ASSERT(rc == 0);
>  
> -        if ( iommu_use_hap_pt(p2m->domain) )
> -        {
> -            if ( iommu_old_flags )
> -                amd_iommu_flush_pages(p2m->domain, gfn, page_order);
> -        }
> -        else if ( need_iommu_pt_sync(p2m->domain) )
> -        {
> -            dfn_t dfn = _dfn(gfn);
> -
> -            if ( iommu_pte_flags )
> -                for ( i = 0; i < (1UL << page_order); i++ )
> -                {
> -                    rc = iommu_map_page(p2m->domain, dfn_add(dfn, i),
> -                                        mfn_add(mfn, i), iommu_pte_flags);
> -                    if ( unlikely(rc) )
> -                    {
> -                        while ( i-- )
> -                            /* If statement to satisfy __must_check. */
> -                            if ( iommu_unmap_page(p2m->domain,
> -                                                  dfn_add(dfn, i)) )
> -                                continue;
> -
> -                        break;
> -                    }
> -                }
> -            else
> -                for ( i = 0; i < (1UL << page_order); i++ )
> -                {
> -                    int ret = iommu_unmap_page(p2m->domain,
> -                                               dfn_add(dfn, i));
> -
> -                    if ( !rc )
> -                        rc = ret;
> -                }
> -        }
> +        if ( need_iommu_pt_sync(p2m->domain) )
> +            rc = iommu_pte_flags ?
> +                iommu_map_page(d, _dfn(gfn), mfn, page_order,
> +                               iommu_pte_flags) :
> +                iommu_unmap_page(d, _dfn(gfn), page_order);
> +        else if ( iommu_use_hap_pt(d) && iommu_old_flags )
> +            amd_iommu_flush_pages(p2m->domain, gfn, page_order);

This logically reverses the
iommu_use_hap_pt(d)/need_iommu_pt_sync(p2m->domain) conditions.

I'd be tempted confine this change to the else if (
need_iommu_pt_sync(p2m->domain) ) block.


Tangentially related, calling amd_iommu_flush_pages() is a laying
violation here because this is supposedly common code.  In reality, it
is the NPT code, so might perhaps be better named as p2m-npt.c.  George?

>      }
>  
>      /*
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index f1df1debc7..3fa559da01 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -718,24 +718,8 @@ p2m_remove_page(struct p2m_domain *p2m, unsigned long 
> gfn_l, unsigned long mfn,
>      p2m_access_t a;
>  
>      if ( !paging_mode_translate(p2m->domain) )
> -    {
> -        int rc = 0;
> -
> -        if ( need_iommu_pt_sync(p2m->domain) )
> -        {
> -            dfn_t dfn = _dfn(mfn);
> -
> -            for ( i = 0; i < (1 << page_order); i++ )
> -            {
> -                int ret = iommu_unmap_page(p2m->domain, dfn_add(dfn, i));
> -
> -                if ( !rc )
> -                    rc = ret;
> -            }
> -        }
> -
> -        return rc;
> -    }
> +        return need_iommu_pt_sync(p2m->domain) ?
> +            iommu_unmap_page(p2m->domain, _dfn(mfn), page_order) : 0;

TBH, I think this is harder to read than the non ternary alternative.

>  
>      ASSERT(gfn_locked_by_me(p2m, gfn));
>      P2M_DEBUG("removing gfn=%#lx mfn=%#lx\n", gfn_l, mfn);
> diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
> index 8b438ae4bc..40db9e7849 100644
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -305,50 +305,71 @@ void iommu_domain_destroy(struct domain *d)
>  }
>  
>  int iommu_map_page(struct domain *d, dfn_t dfn, mfn_t mfn,
> -                   unsigned int flags)
> +                   unsigned int page_order, unsigned int flags)
>  {
>      const struct domain_iommu *hd = dom_iommu(d);
> -    int rc;
> +    unsigned long i;
>  
>      if ( !iommu_enabled || !hd->platform_ops )
>          return 0;
>  
> -    rc = hd->platform_ops->map_page(d, dfn, mfn, flags);
> -    if ( unlikely(rc) )
> +    for ( i = 0; i < (1ul << page_order); i++ )
>      {
> -        if ( !d->is_shutting_down && printk_ratelimit() )
> -            printk(XENLOG_ERR
> -                   "d%d: IOMMU mapping dfn %"PRI_dfn" to mfn %"PRI_mfn" 
> failed: %d\n",
> -                   d->domain_id, dfn_x(dfn), mfn_x(mfn), rc);
> +        int ignored, rc = hd->platform_ops->map_page(d, dfn_add(dfn, i),
> +                                                     mfn_add(mfn, i),
> +                                                     flags);
>  
> -        if ( !is_hardware_domain(d) )
> -            domain_crash(d);
> +        if ( unlikely(rc) )
> +        {
> +            while (i--)

Spaces, but you're also off-by-one when cleaning up i = 0.  Wouldn't it
be easier to reuse iommu_unmap_page() rather than opencode it?

~Andrew

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