From mboxrd@z Thu Jan 1 00:00:00 1970 From: julien.grall@linaro.org (Julien Grall) Date: Tue, 08 Jul 2014 17:53:18 +0100 Subject: [Xen-devel] [PATCH v2 1/3] xen/arm: introduce XENFEAT_grant_map_11 In-Reply-To: <1404835150.25940.9.camel@kazak.uk.xensource.com> References: <1404834132-15847-1-git-send-email-stefano.stabellini@eu.citrix.com> <1404834562.25940.8.camel@kazak.uk.xensource.com> <1404835150.25940.9.camel@kazak.uk.xensource.com> Message-ID: <53BC21FE.2000705@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Ian and Stefano, On 07/08/2014 04:59 PM, Ian Campbell wrote: > On Tue, 2014-07-08 at 16:54 +0100, Stefano Stabellini wrote: >> On Tue, 8 Jul 2014, Ian Campbell wrote: >>> On Tue, 2014-07-08 at 16:42 +0100, Stefano Stabellini wrote: >>>> The flag tells us that the hypervisor maps a grant page to guest >>>> physical address == machine address of the page in addition to the >>>> normal grant mapping address. It is needed to properly issue cache >>>> maintenance operation at the completion of a DMA operation involving a >>>> foreign grant. >>>> >>>> Signed-off-by: Stefano Stabellini >>>> --- >>>> arch/arm/xen/enlighten.c | 6 ++++++ >>>> include/xen/interface/features.h | 3 +++ >>>> 2 files changed, 9 insertions(+) >>>> >>>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c >>>> index b96723e..ee3135a 100644 >>>> --- a/arch/arm/xen/enlighten.c >>>> +++ b/arch/arm/xen/enlighten.c >>>> @@ -262,6 +262,12 @@ static int __init xen_guest_init(void) >>>> xen_domain_type = XEN_HVM_DOMAIN; >>>> >>>> xen_setup_features(); >>>> + >>>> + if (!xen_feature(XENFEAT_grant_map_11)) { >>>> + pr_warn("Please upgrade your Xen.\n" >>>> + "If your platform has any non-coherent DMA devices, they won't work properly.\n"); >>>> + } >>> >>> Unfortunately this isn't quite complete. On a system where all devices >>> are behind an SMMU then we would want to be able to disable the 1:1 >>> workaround, which in turn would imply disabling this feature flag too >>> (since it is no longer necessary and also impossible to implement in >>> that case). >> >> That is true, but in such a system we would have to tell the kernel that >> DMAing is safe, so this will turn into: > > Oh right, yes. Good then ;-) FWIW, I've sent a patch series a couple ago to avoid using swiotlb when the device is protected (see https://patches.linaro.org/25070/). I should take time to rework properly and send a new version. Regards, -- Julien Grall