Re: [Xen-devel] [PATCH v5 1/3] x86/mm: Change default value for suppress #VE in set_mem_access()

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Sep 3, 2018 at 9:48 AM Adrian Pop <apop@xxxxxxxxxxxxxxx> wrote:
>
> From: Vlad Ioan Topan <itopan@xxxxxxxxxxxxxxx>
>
> The default value for the "suppress #VE" bit set by set_mem_access()
> currently depends on whether the call is made from the same domain (the
> bit is set when called from another domain and cleared if called from
> the same domain). This patch changes that behavior to inherit the old
> suppress #VE bit value if it is already set and to set it to 1
> otherwise, which is safer and more reliable.
>
> Signed-off-by: Vlad Ioan Topan <itopan@xxxxxxxxxxxxxxx>
> Signed-off-by: Adrian Pop <apop@xxxxxxxxxxxxxxx>
> ---
>  xen/arch/x86/mm/mem_access.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> index 84d260ebd8..e1522a0b75 100644
> --- a/xen/arch/x86/mm/mem_access.c
> +++ b/xen/arch/x86/mm/mem_access.c
> @@ -284,8 +284,7 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct 
> p2m_domain *hp2m,
>          }
>      }
>
> -    return ap2m->set_entry(ap2m, gfn, mfn, PAGE_ORDER_4K, t, a,
> -                           current->domain != d);

Could you add a comment here saying "inherit the old suppress #VE bit
value if it is already set and to set it to 1 otherwise" to explain
the meaning of the magic -1 value?

Thanks,
Tamas

> +    return ap2m->set_entry(ap2m, gfn, mfn, PAGE_ORDER_4K, t, a, -1);
>  }
>
>  static int set_mem_access(struct domain *d, struct p2m_domain *p2m,
> --
> 2.18.0

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