From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 0/2] KVM: MMU: support VMAs that got remap_pfn_range-ed Date: Mon, 4 Jul 2016 15:37:35 +0800 Message-ID: <577A123F.1060909@linux.intel.com> References: <1467291711-3230-1-git-send-email-pbonzini@redhat.com> <577A049A.4000402@linux.intel.com> <20160704070314.GA13291@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kirti Wankhede , Andrea Arcangeli , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= To: Neo Jia Return-path: In-Reply-To: <20160704070314.GA13291@nvidia.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/04/2016 03:03 PM, Neo Jia wrote: > On Mon, Jul 04, 2016 at 02:39:22PM +0800, Xiao Guangrong wrote: >> >> >> On 06/30/2016 09:01 PM, Paolo Bonzini wrote: >>> The vGPU folks would like to trap the first access to a BAR by setting >>> vm_ops on the VMAs produced by mmap-ing a VFIO device. The fault handler >>> then can use remap_pfn_range to place some non-reserved pages in the VMA. >> >> Why does it require fetching the pfn when the fault is triggered rather >> than when mmap() is called? > > Hi Guangrong, > > as such mapping information between virtual mmio to physical mmio is only available > at runtime. Sorry, i do not know what the different between mmap() and the time VM actually accesses the memory for your case. Could you please more detail? > >> >> Why the memory mapped by this mmap() is not a portion of MMIO from >> underlayer physical device? If it is a valid system memory, is this interface >> really needed to implemented in vfio? (you at least need to set VM_MIXEDMAP >> if it mixed system memory with MMIO) >> > > It actually is a portion of the physical mmio which is set by vfio mmap. So i do not think we need to care its refcount, i,e, we can consider it as reserved_pfn, Paolo? > >> IIUC, the kernel assumes that VM_PFNMAP is a continuous memory, e.g, like >> current KVM and vaddr_get_pfn() in vfio, but it seems nvdia's patchset >> breaks this semantic as ops->validate_map_request() can adjust the physical >> address arbitrarily. (again, the name 'validate' should be changed to match >> the thing as it is really doing) > > The vgpu api will allow you to adjust the target mmio address and the size via > validate_map_request, but it is still physical contiguous as . Okay, the interface confused us, maybe this interface need to be cooked to reflect to this fact. Thanks!