Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753940AbaJCQeM (ORCPT ); Fri, 3 Oct 2014 12:34:12 -0400 Received: from smtp.citrix.com ([66.165.176.89]:19258 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753631AbaJCQeL (ORCPT ); Fri, 3 Oct 2014 12:34:11 -0400 X-IronPort-AV: E=Sophos;i="5.04,648,1406592000"; d="scan'208";a="177948023" Message-ID: <1412354047.12695.38.camel@citrix.com> Subject: Re: [PATCH v2 2/2] xen/arm: introduce GNTTABOP_cache_flush From: Ian Campbell To: Stefano Stabellini CC: David Vrabel , , , , Date: Fri, 3 Oct 2014 17:34:07 +0100 In-Reply-To: References: <1412348006-27884-2-git-send-email-stefano.stabellini@eu.citrix.com> <542EBB2A.6030104@citrix.com> Organization: Citrix Systems, Inc. Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.6-1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2014-10-03 at 17:20 +0100, Stefano Stabellini wrote: > On Fri, 3 Oct 2014, David Vrabel wrote: > > On 03/10/14 15:53, Stefano Stabellini wrote: > > > Introduce support for new hypercall GNTTABOP_cache_flush. > > > Use it to perform cache flashing on pages used for dma when necessary. > > [..] > > > /* functions called by SWIOTLB */ > > > @@ -22,16 +25,31 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset, > > > size_t len = left; > > > void *vaddr; > > > > > > + if (len + offset > PAGE_SIZE) > > > + len = PAGE_SIZE - offset; > > > + > > > if (!pfn_valid(pfn)) > > > { > > > - /* TODO: cache flush */ > > > + struct gnttab_cache_flush cflush; > > > + > > > + cflush.op = 0; > > > + cflush.a.dev_bus_addr = pfn << PAGE_SHIFT; > > > + cflush.offset = offset; > > > + cflush.size = len; > > > + > > > + if (op == dmac_unmap_area && dir != DMA_TO_DEVICE) > > > + cflush.op = GNTTAB_CACHE_INVAL; > > > + if (op == dmac_map_area) { > > > + cflush.op = GNTTAB_CACHE_CLEAN; > > > + if (dir == DMA_FROM_DEVICE) > > > + cflush.op |= GNTTAB_CACHE_INVAL; > > > + } > > > > Are all these cache operations needed? You do a clean on map regardless > > of the direction and INVAL on map seems unnecessary. Isn't the inval on map so that the processor doesn't decide to evict/clean the cache line all over your newly DMA'd data? > > I would have thought it would be: > > > > map && (TO_DEVICE || BOTH) > > op = CLEAN > > > > unmap && (FROM_DEVICE || BOTH) > > op = INVAL > > I was trying to do the same thing Linux is already doing on native to > stay on the safe side. > > See arch/arm/mm/cache-v7.S:v7_dma_map_area and > arch/arm/mm/cache-v7.S:v7_dma_unmap_area. > > Unless I misread the assembly they should match. I think you have, beq doesn't set lr, so the called function will return to its "grandparent". i.e. the caller of v7_dma_map_area in this case (which will have used bl), so: ENTRY(v7_dma_map_area) add r1, r1, r0 teq r2, #DMA_FROM_DEVICE beq v7_dma_inv_range b v7_dma_clean_range ENDPROC(v7_dma_map_area) Is actually if (dir == from device) inv else clean which makes much more sense I think. > > > > > --- a/include/xen/interface/grant_table.h > > > +++ b/include/xen/interface/grant_table.h > > > @@ -479,6 +479,24 @@ struct gnttab_get_version { > > > DEFINE_GUEST_HANDLE_STRUCT(gnttab_get_version); > > > > > > /* > > > + * Issue one or more cache maintenance operations on a portion of a > > > + * page granted to the calling domain by a foreign domain. > > > + */ > > > +#define GNTTABOP_cache_flush 12 > > > +struct gnttab_cache_flush { > > > + union { > > > + uint64_t dev_bus_addr; > > > + grant_ref_t ref; > > > + } a; > > > + uint32_t offset; /* offset from start of grant */ > > > + uint32_t size; /* size within the grant */ > > > +#define GNTTAB_CACHE_CLEAN (1<<0) > > > +#define GNTTAB_CACHE_INVAL (1<<1) > > > + uint32_t op; > > > +}; > > > +DEFINE_GUEST_HANDLE_STRUCT(gnttab_cache_flush); > > > + > > > +/* > > > * Bitfield values for update_pin_status.flags. > > > */ > > > /* Map the grant entry for access by I/O devices. */ > > > > If the ARM bits are correct, have a > > > > Reviewed-by: David Vrabel > > > > for the common header. > > > > David > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/