x86 pv: Insufficient care with non-coherent mappings

ISSUE DESCRIPTION Xen maintains a type reference count for pages, in addition to a regular reference count. This scheme is used to maintain invariants required for Xen's safety, e.g. PV guests may not have direct writeable access to pagetables; updates need auditing by Xen. Unfortunately, Xen's...

x86: PV kernel context switch corruption

ISSUE DESCRIPTION On hardware supporting the fsgsbase feature, 64bit PV guests can set and clear the applicable control bit in its virtualised %cr4, but the feature remains fully active in hardware. Therefore, the associated instructions are actually usable. Linux, which does not currently suppor...