On 15 June 2018 at 14:37, Laszlo Ersek <lersek@xxxxxxxxxx> wrote: > 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. > OK, so I was using the wrong -device, using just 'ramfb' works fine. > I'll try to come back with test results too. > Thanks! >> >> 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
