On Thu, May 21, 2020 at 10:43:58PM +0100, Igor Druzhinin wrote: > If a recalculation NPT fault hasn't been handled explicitly in > hvm_hap_nested_page_fault() then it's potentially safe to retry - > US bit has been re-instated in PTE and any real fault would be correctly > re-raised next time. > > This covers a specific case of migration with vGPU assigned on AMD: > global log-dirty is enabled and causes immediate recalculation NPT > fault in MMIO area upon access. This type of fault isn't described > explicitly in hvm_hap_nested_page_fault (this isn't called on > EPT misconfig exit on Intel) which results in domain crash.
Couldn't direct MMIO regions be handled like other types of memory for the purposes of logdiry mode? I assume there's already a path here used for other memory types when logdirty is turned on, and hence would seem better to just make direct MMIO regions also use that path? > Signed-off-by: Igor Druzhinin <igor.druzhi...@citrix.com> > --- > xen/arch/x86/hvm/svm/svm.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c > index 46a1aac..f0d0bd3 100644 > --- a/xen/arch/x86/hvm/svm/svm.c > +++ b/xen/arch/x86/hvm/svm/svm.c > @@ -1726,6 +1726,10 @@ static void svm_do_nested_pgfault(struct vcpu *v, > /* inject #VMEXIT(NPF) into guest. */ > nestedsvm_vmexit_defer(v, VMEXIT_NPF, pfec, gpa); > return; > + case 0: > + /* If a recalculation page fault hasn't been handled - just retry. */ > + if ( pfec & PFEC_user_mode ) > + return; I'm slightly worried that this diverges from the EPT implementation now, in the sense that returning 0 from hvm_hap_nested_page_fault will no longer trigger a guest crash. Thanks, Roger.
