Regular oops on shutdown of KVM/ARM64 machines with VGA device

On 30/06/15 08:54, Dirk M?ller wrote:

Hi Marc,

quoted

Also, care to provide some hints about your kernel configuration?

I believe the relevant parameters are:

CONFIG_PGTABLE_LEVELS=4
# CONFIG_ARM64_64K_PAGES is not set
# CONFIG_ARM64_VA_BITS_39 is not set
CONFIG_ARM64_VA_BITS_48=y
CONFIG_ARM64_VA_BITS=48
CONFIG_KVM_MMIO=y
CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=y
CONFIG_KVM_COMPAT=y
CONFIG_VIRTUALIZATION=y
CONFIG_KVM=y
CONFIG_KVM_ARM_HOST=y
CONFIG_KVM_ARM_MAX_VCPUS=4


the full config is here: http://pastebin.com/raw.php?i=GKAaVLYE

quoted

What is the VGA device you mention in $subject?
A QEMU command line so that we can try and reproduce the issue you're
seeing?

with qemu 2.3.0:

qemu-system-aarch64 --enable-kvm -M virt -cpu host -vnc :4 -bios
/usr/share/qemu/qemu-uefi-aarch64.bin -m 1G -device VGA

then connecting to the vnc to cause the VGA device to be initialized,
and then simply ctrl-c'ing the qemu process, you'll get this crash
100% of each and every time. If you want additional debug output or
try out something, just let me know and I'll be happy to provide you
with it.

Can try the following patch?

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 7b42012..d902a53 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c

@@ -109,7 +109,7 @@ static void kvm_flush_dcache_pud(pud_t pud)
  */
 static void stage2_dissolve_pmd(struct kvm *kvm, phys_addr_t addr, pmd_t *pmd)
 {
-	if (!kvm_pmd_huge(*pmd))
+	if (pmd_none(*pmd) || !kvm_pmd_huge(*pmd))
 		return;
 
 	pmd_clear(pmd);

It seems to fix the issue for me, though with a relatively different
configuration.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...