On 15/05/2015 17:12, Christoffer Dall wrote: >>> > > Can you find out what memory attributes the guest is using for the >>> > > memory---and if it's uncached, why? >> > >> > For USB, see "drivers/usb/core/hcd-pci.c", function usb_hcd_pci_probe(): >> > it uses ioremap_nocache(). >> > >> > On the "why", that ioremap_nocache() call can be tracked to >> > >> > http://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/?id=a914dd8b >> > >> > (Feb 2002), which predates the kernel's move to git. I guess >> > ioremap_nocache() is used simply because USB host controllers are >> > supposed to programmed like that. >> > >> > And, from "arch/arm64/include/asm/io.h": >> > >> > #define ioremap_nocache(addr, size) __ioremap((addr), (size), >> > __pgprot(PROT_DEVICE_nGnRE)) >> > > So this just means that these devices should be mapped as device memory > (like the VGA case before) right? And therefore should work with Drew's > patches (assuming they are actually correct and you add the right QEMU > annotations to set the memory regions and non-cacheable), correct? As far as I understand ioremap_nocache() is used on a MMIO BAR. QEMU does not back those with RAM at all, each access causes a userspace exit. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
