On 06/15/18 12:48, Ard Biesheuvel wrote: > KVM guests on ARM have special requirements when it comes to mapping > framebuffers: given that the host [emulating the framebuffer] uses > cacheable accesses to read from the framebuffer region, the guest > should uses cacheable accesses as well, or coherency is lost, i.e., > the host does not see what the guest writes. > > Modifying PCI drivers to take this into account just for KVM on ARM is > unreasonable, given that mapping BARs cacheable and still expecting > side effects does not make any sense. However, doing the same for > regions of system memory does make sense, since a framebuffer in DRAM > could be accessed via DMA by a coherent master, and so it makes sense > to take the memory attributes described by the UEFI memory map into > account if it covers the efifb region. > > Patch #2 implements this. Patch #1 is a preparatory patch that makes > efi_mem_desc_lookup() usable for us in #2. > > Question is how to best test this. I tried Gerd's ramfb patches against > QEMU with a recent ArmVirtQemu build but I am having trouble getting my > console to use the EFI framebuffer. What command line did you use? From my earlier testing (which obviously couldn't include your present patches): http://mid.mail-archive.com/0da06062-431e-385e-0b00-577f1daf3a1e@xxxxxxxxxx the important options are "-nodefaults" plus "-device ramfb". This makes sure that no hardware appears in the VM that the Linux guest could consider "video hardware" in its own right. So the only console possibility will be efifb, and no other (more specific / higher prio) fb driver will be able to eject it. I'll try to come back with test results too. Thanks Laszlo > > Ard Biesheuvel (2): > efi: drop type and attribute checks in efi_mem_desc_lookup() > fbdev/efifb: honour UEFI memory map attributes when mapping the fb > > arch/x86/platform/efi/quirks.c | 3 +- > drivers/firmware/efi/efi.c | 8 +-- > drivers/firmware/efi/esrt.c | 5 +- > drivers/video/fbdev/efifb.c | 52 ++++++++++++++++---- > 4 files changed, 49 insertions(+), 19 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
