From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zoltan Kiss Subject: Re: [PATCH net-next v3 2/9] xen-netback: Change TX path from grant copy to mapping Date: Fri, 10 Jan 2014 15:24:04 +0000 Message-ID: <52D01094.5060102@citrix.com> References: <1389139818-24458-1-git-send-email-zoltan.kiss@citrix.com> <1389139818-24458-3-git-send-email-zoltan.kiss@citrix.com> <20140109153015.GF12164@zion.uk.xensource.com> <52CFDAEC.5080708@citrix.com> <20140110114534.GE29180@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , To: Wei Liu Return-path: In-Reply-To: <20140110114534.GE29180@zion.uk.xensource.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 10/01/14 11:45, Wei Liu wrote: > On Fri, Jan 10, 2014 at 11:35:08AM +0000, Zoltan Kiss wrote: > [...] >> >>>> @@ -920,6 +852,18 @@ static int xenvif_tx_check_gop(struct xenvif *vif, >>>> err = gop->status; >>>> if (unlikely(err)) >>>> xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR); >>>> + else { >>>> + if (vif->grant_tx_handle[pending_idx] != >>>> + NETBACK_INVALID_HANDLE) { >>>> + netdev_err(vif->dev, >>>> + "Stale mapped handle! pending_idx %x handle %x\n", >>>> + pending_idx, vif->grant_tx_handle[pending_idx]); >>>> + BUG(); >>>> + } >>>> + set_phys_to_machine(idx_to_pfn(vif, pending_idx), >>>> + FOREIGN_FRAME(gop->dev_bus_addr >> PAGE_SHIFT)); >>> >>> What happens when you don't have this? >> Your frags will be filled with garbage. I don't understand exactly >> what this function does, someone might want to enlighten us? I've >> took it's usage from classic kernel. >> Also, it might be worthwhile to check the return value and BUG if >> it's false, but I don't know what exactly that return value means. >> > > This is actually part of gnttab_map_refs. As you're using hypercall > directly this becomes very fragile. > > So the right thing to do is to fix gnttab_map_refs. I agree, as I mentioned in other email in this thread, I think that should be the topic of an another patchseries. In the meantime, I will use gnttab_batch_map instead of the direct hypercall, it handles the GNTST_eagain scenario, and I will use set_phys_to_machine the same way as m2p_override does: if (unlikely(!set_phys_to_machine(idx_to_pfn(vif, pending_idx), FOREIGN_FRAME(gop->dev_bus_addr >> PAGE_SHIFT)) BUG(); Zoli