[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM_IO vmas
On Fri, Oct 22, 2010 at 02:02:31PM -0400, Konrad Rzeszutek Wilk wrote: > On Fri, Oct 22, 2010 at 09:44:08AM -0700, H. Peter Anvin wrote: > > On 10/22/2010 08:08 AM, Konrad Rzeszutek Wilk wrote: > > >> > > >> Okay, could you clarify this part a bit? Why does the kernel need to > > >> know the difference between "pseudo-physical" and "machine addresses" at > > >> all? If they overlap, there is a problem, and if they don't overlap, it > > >> will be a 1:1 mapping anyway... > > > > > > The flag (_PAGE_IOMAP) is used when we set the PTE so that the MFN value > > > is > > > used instead of the PFN. We need that b/c when a driver does page_to_pfn() > > > it ends up using the PFN as bus address to write out registers data. > > > > > > Without this patch, the page->virt->PFN value is used and the PFN != to > > > real MFN > > > so we end up writing in a memory address that the PCI device has no idea > > > about. > > > By setting the PTE with the MFN, the virt->PFN gets the real MFN value. > > > > > > The drivers I am talking about are mostly, if not all, located in > > > drivers/gpu > > > and it looks that we are missing two more patches to utilize the patch > > > that Jeremy posted. > > > > > > Please note that I am _not_ suggesting that the two patches > > > below should go out - I still need to post them on drm mailing list. > > > > > > > I'm still seriously confused. If I understand this correctly, we're > > talking about DMA addresses here (as opposed to PIO addresses, i.e. > > BARs), right? > > Correct. The BARs are ok since they go through the ioremap. Whoops. I answered that incorrectly. No, we are not talking about BARs. The BARs are ok (look at x86/PCI: make sure _PAGE_IOMAP it set on pci mappings patch, http://amailbox.org/mailarchive/linux-kernel/2010/10/12/4630930/thread) We are talking about the GPU's VM engine (or the GART on the Northbridge). _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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