Re: [Xen-devel] [PATCH v5 2/3] x86/altp2m: Add a hvmop for setting the suppress #VE bit

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 09/03/2018 04:48 PM, Adrian Pop wrote:
> Introduce a new hvmop, HVMOP_altp2m_set_suppress_ve, which allows a
> domain to change the value of the #VE suppress bit for a page.
> 
> Add a libxc wrapper for invoking this hvmop.
> 
> Signed-off-by: Adrian Pop <apop@xxxxxxxxxxxxxxx>
> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

Sorry I haven't had a chance to weigh in on this one yet.  A couple fo
comments...


> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> index e1522a0b75..4d49025cbe 100644
> --- a/xen/arch/x86/mm/mem_access.c
> +++ b/xen/arch/x86/mm/mem_access.c
> @@ -495,6 +495,61 @@ void arch_p2m_set_access_required(struct domain *d, bool 
> access_required)
>      }
>  }
>  
> +/*
> + * Set/clear the #VE suppress bit for a page.  Only available on VMX.
> + */
> +int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, bool suppress_ve,
> +                        unsigned int altp2m_idx)

This should clearly be in p2m.c, and...

> +{
> +    struct p2m_domain *host_p2m = p2m_get_hostp2m(d);
> +    struct p2m_domain *ap2m = NULL;
> +    struct p2m_domain *p2m;
> +    mfn_t mfn;
> +    p2m_access_t a;
> +    p2m_type_t t;
> +    int rc;
> +
> +    if ( !cpu_has_vmx_virt_exceptions )
> +        return -EOPNOTSUPP;

We should avoid Intel-specific checks in common code.

In fact, this is wrong, because you can choose to run a guest in shadow
mode even on a system with virt exceptions -- in which case you'd
trigger the ASSERT() in p2m-pt.c:p2m_pt_set_entry().

Probably what should happen is that we should move the vmx check into
p2m-ept.c:p2m_ept_set_entry(), and replace the ASSERT(sve = 0) in
p2m-pt.c:p2m_pt_set_entry() with "if ( sve != 0 ) return -ENOTSUPP;".

Although what should probably *really* happen is that
`HVMOP_altp2m_vcpu_enable_notify` should fail with -EOPNOTSUPP instead
of silently succeeding.

Everything else looks good.

I realize this has been checked in already; no need to revert if you can
send a follow-up patch in the next couple of (business) days.

Thanks,
 -George

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