Re: [PATCH v2 1/6] x86: support cache-writeback in flush_area_local() et al

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, May 03, 2023 at 11:44:39AM +0200, Jan Beulich wrote:
> The majority of the present callers really aren't after invalidating
> cache contents, but only after writeback. Make this available by simply
> extending the FLUSH_CACHE handling accordingly. No feature checks are
> required here: cache_writeback() falls back to cache_flush() as
> necessary, while WBNOINVD degenerates to WBINVD on older hardware.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> ---
> v2: FLUSH_WRITEBACK -> FLUSH_CACHE_WRITEBACK.
> 
> --- a/xen/arch/x86/flushtlb.c
> +++ b/xen/arch/x86/flushtlb.c
> @@ -232,7 +232,7 @@ unsigned int flush_area_local(const void
>      if ( flags & FLUSH_HVM_ASID_CORE )
>          hvm_flush_guest_tlbs();
>  
> -    if ( flags & FLUSH_CACHE )
> +    if ( flags & (FLUSH_CACHE | FLUSH_CACHE_WRITEBACK) )
>      {
>          const struct cpuinfo_x86 *c = &current_cpu_data;
>          unsigned long sz = 0;
> @@ -245,13 +245,16 @@ unsigned int flush_area_local(const void
>               c->x86_clflush_size && c->x86_cache_size && sz &&
>               ((sz >> 10) < c->x86_cache_size) )
>          {
> -            cache_flush(va, sz);
> -            flags &= ~FLUSH_CACHE;
> +            if ( flags & FLUSH_CACHE )
> +                cache_flush(va, sz);
> +            else
> +                cache_writeback(va, sz);
> +            flags &= ~(FLUSH_CACHE | FLUSH_CACHE_WRITEBACK);
>          }
> -        else
> -        {
> +        else if ( flags & FLUSH_CACHE )
>              wbinvd();
> -        }
> +        else
> +            wbnoinvd();
>      }
>  
>      if ( flags & FLUSH_ROOT_PGTBL )
> --- a/xen/arch/x86/include/asm/flushtlb.h
> +++ b/xen/arch/x86/include/asm/flushtlb.h
> @@ -135,6 +135,8 @@ void switch_cr3_cr4(unsigned long cr3, u
>  #else
>  # define FLUSH_NO_ASSIST 0
>  #endif
> + /* Write back data cache contents */
> +#define FLUSH_CACHE_WRITEBACK  0x10000
>  
>  /* Flush local TLBs/caches. */
>  unsigned int flush_area_local(const void *va, unsigned int flags);
> @@ -194,7 +196,11 @@ static inline int clean_and_invalidate_d
>  }
>  static inline int clean_dcache_va_range(const void *p, unsigned long size)
>  {
> -    return clean_and_invalidate_dcache_va_range(p, size);
> +    unsigned int order = get_order_from_bytes(size);
> +
> +    /* sub-page granularity support needs to be added if necessary */
> +    flush_area_local(p, FLUSH_CACHE_WRITEBACK | FLUSH_ORDER(order));
> +    return 0;
>  }

I'm planning to get rid of the clean_dcache_va_range() helper on x86,
but I don't want to force you to rebase on top of that.

Thanks, Roger.