kvm: x86: Return LA57 feature based on hardware capability
authorYu Zhang <yu.c.zhang@linux.intel.com>
Thu, 31 Jan 2019 16:09:43 +0000 (00:09 +0800)
committerPaolo Bonzini <pbonzini@redhat.com>
Fri, 22 Feb 2019 18:25:05 +0000 (19:25 +0100)
commit511da98d207d5c0675a10351b01e37cbe50a79e5
treee688f8fe345665af98863606f6eb38174a4fc3e9
parentad7dc69aeb23138cc23c406cac25003b97e8ee17
kvm: x86: Return LA57 feature based on hardware capability

Previously, 'commit 372fddf70904 ("x86/mm: Introduce the 'no5lvl' kernel
parameter")' cleared X86_FEATURE_LA57 in boot_cpu_data, if Linux chooses
to not run in 5-level paging mode. Yet boot_cpu_data is queried by
do_cpuid_ent() as the host capability later when creating vcpus, and Qemu
will not be able to detect this feature and create VMs with LA57 feature.

As discussed earlier, VMs can still benefit from extended linear address
width, e.g. to enhance features like ASLR. So we would like to fix this,
by return the true hardware capability when Qemu queries.

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
arch/x86/kvm/cpuid.c