On 15 June 2018 at 18:39, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > On 15 June 2018 at 18:38, 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. >>> >>> 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(-) >>> >> >> I reproduced the issue using the latest stock F28 kernel in the KVM >> guest, on my Mustang A3 host. Then I built this set on top of >> v4.17-12074-g4c5e8fc62d6a, using the F28 kernel config. I didn't pass >> any parameters to efifb. The series works perfectly for me. >> >> Tested-by: Laszlo Ersek <lersek@xxxxxxxxxx> >> > > Thanks! Very happy to hear that ... Peter, any objections? If not, I will resend them with Laszlo's T-b and cc the fbdev list and maintainer to get this into v4.19 Thanks, Ard. -- 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
