Hi: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > On Thu, Feb 06, 2020 at 12:32:38PM +0100, Vitaly Kuznetsov wrote: >> linmiaohe <linmiaohe@xxxxxxxxxx> writes: >> >> >> I have to admit that shadow MMU in KVM is not my strong side but this >> comment reads weird, I'd appreciate if someone could suggest a better >> alternative. > > /* One off flag for a stupid corner case in shadow paging. */ >> >> > */ > > /* > * Indicates the guest is trying to write a gfn that contains one or > * more of the PTEs used to translate the write itself, i.e. the access > * is changing its own translation in the guest page tables. KVM exits > * to userspace if emulation of the faulting instruction fails and this > * flag is set, as KVM cannot make forward progress. > * > * If emulation fails for a write to guest page tables, KVM unprotects > * (zaps) the shadow page for the target gfn and resumes the guest to > * retry the non-emulatable instruction (on hardware). Unprotecting the > * gfn doesn't allow forward progress for a self-changing access because > * doing so also zaps the translation for the gfn, i.e. retrying the > * instruction will hit a !PRESENT fault, which results in a new shadow > * page and sends KVM back to square one. > */ >> > bool write_fault_to_shadow_pgtable; Thanks for your detail comment. This field confused me once. Thanks to both for review! Will send v2.
