Re: [Xen-devel] [PATCH 2/2] x86: use invpcid to do global flushing

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.03.18 at 10:50, <wei.liu2@xxxxxxxxxx> wrote:
> @@ -120,11 +121,24 @@ unsigned int flush_area_local(const void *va, unsigned 
> int flags)
>          else
>          {
>              u32 t = pre_flush();
> -            unsigned long cr4 = read_cr4();
>  
> -            write_cr4(cr4 & ~X86_CR4_PGE);
> -            barrier();
> -            write_cr4(cr4);
> +            if ( !cpu_has_invpcid )
> +            {
> +                unsigned long cr4 = read_cr4();
> +
> +                write_cr4(cr4 & ~X86_CR4_PGE);
> +                barrier();
> +                write_cr4(cr4);
> +            }
> +            else
> +            {
> +                /*
> +                 * Using invpcid to flush all mappings works
> +                 * regardless of whether PCID is enabled or not.
> +                 * It is faster than read-modify-write CR4.
> +                 */
> +                invpcid_flush_all();
> +            }

As just validly indicated by Jürgen, this is where my comment I
gave to one of his patches actually belongs: This is correct for
FLUSH_TLB_GLOBAL, but goes too far for FLUSH_TLB.

Jan

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