linux-kernel - Re: [PATCH] x86/xen: support priv-mapping in an HVM tools domain

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Date:   Thu, 19 Oct 2017 13:45:03 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Paul Durrant <paul.durrant@...rix.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/xen: support priv-mapping in an HVM tools domain

On 10/19/2017 11:26 AM, Paul Durrant wrote:
> If the domain has XENFEAT_auto_translated_physmap then use of the PV-
> specific HYPERVISOR_mmu_update hypercall is clearly incorrect.
>
> This patch adds checks in xen_remap_domain_gfn_array() and
> xen_unmap_domain_gfn_array() which call through to the approprate
> xlate_mmu function if the feature is present. A check is also added
> to xen_remap_domain_gfn_range() to fail with -EOPNOTSUPP since this
> should not be used in an HVM tools domain.
>
> Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> ---
>  arch/x86/xen/mmu.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 3e15345abfe7..d33e7dbe3129 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -172,6 +172,9 @@ int xen_remap_domain_gfn_range(struct vm_area_struct *vma,
>  			       pgprot_t prot, unsigned domid,
>  			       struct page **pages)
>  {
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return -EOPNOTSUPP;
> +

This is never called on XENFEAT_auto_translated_physmap domains, there
is a check in privcmd_ioctl_mmap() for that.

>  	return do_remap_gfn(vma, addr, &gfn, nr, NULL, prot, domid, pages);
>  }
>  EXPORT_SYMBOL_GPL(xen_remap_domain_gfn_range);
> @@ -182,6 +185,10 @@ int xen_remap_domain_gfn_array(struct vm_area_struct *vma,
>  			       int *err_ptr, pgprot_t prot,
>  			       unsigned domid, struct page **pages)
>  {
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return xen_xlate_remap_gfn_array(vma, addr, gfn, nr, err_ptr,
> +						 prot, domid, pages);
> +

So how did this work before? In fact, I don't see any callers of
xen_xlate_{re|un}map_gfn_range().

-boris


>  	/* We BUG_ON because it's a programmer error to pass a NULL err_ptr,
>  	 * and the consequences later is quite hard to detect what the actual
>  	 * cause of "wrong memory was mapped in".
> @@ -193,9 +200,12 @@ EXPORT_SYMBOL_GPL(xen_remap_domain_gfn_array);
>  
>  /* Returns: 0 success */
>  int xen_unmap_domain_gfn_range(struct vm_area_struct *vma,
> -			       int numpgs, struct page **pages)
> +			       int nr, struct page **pages)
>  {
> -	if (!pages || !xen_feature(XENFEAT_auto_translated_physmap))
> +	if (xen_feature(XENFEAT_auto_translated_physmap))
> +		return xen_xlate_unmap_gfn_range(vma, nr, pages);
> +
> +	if (!pages)
>  		return 0;
>  
>  	return -EINVAL;