Re: [Xen-devel] [PATCH 02/11] VMX: implement suppress #VE.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/01/15 21:26, Ed White wrote:
> In preparation for selectively enabling hardware #VE in a later patch,
> set suppress #VE on all EPTE's on #VE-capable hardware.
>
> Suppress #VE should always be the default condition for two reasons:
> it is generally not safe to deliver #VE into a guest unless that guest
> has been modified to receive it; and even then for most EPT violations only
> the hypervisor is able to handle the violation.
>
> Signed-off-by: Ed White <edmund.h.white@xxxxxxxxx>
> ---
>  xen/arch/x86/mm/p2m-ept.c         | 34 +++++++++++++++++++++++++++++++++-
>  xen/include/asm-x86/hvm/vmx/vmx.h |  1 +
>  2 files changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> index eb8b5f9..2b9f07c 100644
> --- a/xen/arch/x86/mm/p2m-ept.c
> +++ b/xen/arch/x86/mm/p2m-ept.c
> @@ -41,7 +41,7 @@
>  #define is_epte_superpage(ept_entry)    ((ept_entry)->sp)
>  static inline bool_t is_epte_valid(ept_entry_t *e)
>  {
> -    return (e->epte != 0 && e->sa_p2mt != p2m_invalid);
> +    return (e->valid != 0 && e->sa_p2mt != p2m_invalid);
>  }
>  
>  /* returns : 0 for success, -errno otherwise */
> @@ -194,6 +194,19 @@ static int ept_set_middle_entry(struct p2m_domain *p2m, 
> ept_entry_t *ept_entry)
>  
>      ept_entry->r = ept_entry->w = ept_entry->x = 1;
>  
> +    /* Disable #VE on all entries */ 
> +    if ( cpu_has_vmx_virt_exceptions )
> +    {
> +        ept_entry_t *table = __map_domain_page(pg);
> +
> +        for ( int i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )

Style - please declare i in the upper scope, and it should be unsigned.

> +            table[i].suppress_ve = 1;
> +
> +        unmap_domain_page(table);
> +
> +        ept_entry->suppress_ve = 1;
> +    }
> +
>      return 1;
>  }
>  
> @@ -243,6 +256,10 @@ static int ept_split_super_page(struct p2m_domain *p2m, 
> ept_entry_t *ept_entry,
>          epte->sp = (level > 1);
>          epte->mfn += i * trunk;
>          epte->snp = (iommu_enabled && iommu_snoop);
> +
> +        if ( cpu_has_vmx_virt_exceptions )
> +            epte->suppress_ve = 1;
> +
>          ASSERT(!epte->rsvd1);
>  
>          ept_p2m_type_to_flags(epte, epte->sa_p2mt, epte->access);
> @@ -753,6 +770,9 @@ ept_set_entry(struct p2m_domain *p2m, unsigned long gfn, 
> mfn_t mfn,
>          ept_p2m_type_to_flags(&new_entry, p2mt, p2ma);
>      }
>  
> +    if ( cpu_has_vmx_virt_exceptions )
> +        new_entry.suppress_ve = 1;
> +
>      rc = atomic_write_ept_entry(ept_entry, new_entry, target);
>      if ( unlikely(rc) )
>          old_entry.epte = 0;
> @@ -1069,6 +1089,18 @@ int ept_p2m_init(struct p2m_domain *p2m)
>      /* set EPT page-walk length, now it's actual walk length - 1, i.e. 3 */
>      ept->ept_wl = 3;
>  
> +    /* Disable #VE on all entries */
> +    if ( cpu_has_vmx_virt_exceptions )
> +    {
> +        ept_entry_t *table =
> +            map_domain_page(pagetable_get_pfn(p2m_get_pagetable(p2m)));
> +
> +        for ( int i = 0; i < EPT_PAGETABLE_ENTRIES; i++ )
> +            table[i].suppress_ve = 1;

Is it safe setting SVE on an entry which is not known to be a superpage
or not present?  The manual states that the bit is ignored in this case,
but I am concerned that, as with SVE, this bit will suddenly gain
meaning in the future.

> +
> +        unmap_domain_page(table);
> +    }
> +
>      if ( !zalloc_cpumask_var(&ept->synced_mask) )
>          return -ENOMEM;
>  
> diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h 
> b/xen/include/asm-x86/hvm/vmx/vmx.h
> index 8bae195..70fee74 100644
> --- a/xen/include/asm-x86/hvm/vmx/vmx.h
> +++ b/xen/include/asm-x86/hvm/vmx/vmx.h
> @@ -49,6 +49,7 @@ typedef union {
>          suppress_ve :   1;  /* bit 63 - suppress #VE */
>      };
>      u64 epte;
> +    u64 valid       :   63; /* entire EPTE except suppress #VE bit */

I am not sure 'valid' is a sensible name here.  As it is only used in
is_epte_valid(), might it be better to just use ->epte and a bitmask for
everything other than the #VE bit?

~Andrew

>  } ept_entry_t;
>  
>  typedef struct {



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