On 22/05/2020 11:23, Roger Pau Monné wrote: > On Fri, May 22, 2020 at 11:14:24AM +0100, Igor Druzhinin wrote: >> On 22/05/2020 11:08, Roger Pau Monné wrote: >>> 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? >> >> The proble of handling only MMIO case is that the issue still stays. >> It will be hit with some other memory type since it's not MMIO specific. >> The issue is that if global recalculation is called, the next hit to >> this type will cause a transient fault which will not be handled >> correctly after a due fixup by neither of our handlers. > > I admit I should go look at the code, but for example RAM p2m types > don't require this fix, so I assume there's some different path taken > in that case that avoids all this? > > Ie: when global logdirty is enabled you will start to get nested page > faults for every access, yet only direct MMIO types require this fix?
It's not "only MMIO" - it's just MMIO area is hit in my particular case. I'd prefer this fix to address the general issue otherwise for SVM we would have to write handlers in hvm_hap_nested_page_fault() for every case as soon as we hit it. Igor
