Re: [PATCH v2 for-4.7 4/5] x86/svm: Don't unconditionally use a new ASID in svm_invlpg_intercept()

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 05/09/2016 02:27 PM, Andrew Cooper wrote:
> paging_invlpg() already returns a boolean indicating whether an invalidation
> is necessary or not.  A return value of 0 indicates that the specified virtual
> address wasn't shadowed (or has already been flushed), cannot currently be
> cached in the TLB.
>
> This is a performance optimisation.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Tim Deegan <tim@xen.org>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>
> While being a performance optimisation, the main purpose of splitting this
> patch out is to separate the functional change.  The following patch performs
> some function shuffling, and this patch makes the following one more obviously
> correct.
>
> v2:
>  * Newly split out
> ---
>  xen/arch/x86/hvm/svm/svm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index 7634c3f..081a5d8 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -2224,8 +2224,8 @@ static void svm_invlpg_intercept(unsigned long vaddr)
>  {
>      struct vcpu *curr = current;
>      HVMTRACE_LONG_2D(INVLPG, 0, TRC_PAR_LONG(vaddr));
> -    paging_invlpg(curr, vaddr);
> -    svm_asid_g_invlpg(curr, vaddr);
> +    if ( paging_invlpg(curr, vaddr) )
> +        svm_asid_g_invlpg(curr, vaddr);
>  }
>  
>  static struct hvm_function_table __initdata svm_function_table = {


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