On 18.02.2021 14:25, Julien Grall wrote: > Hi, > > On 18/02/2021 13:05, Jan Beulich wrote: >> On 17.02.2021 17:07, Julien Grall wrote: >>> On 17/02/2021 15:01, Jan Beulich wrote: >>>> On 17.02.2021 15:24, Julien Grall wrote: >>>>> From: Julien Grall <jgr...@amazon.com> >>>>> >>>>> The new x86 IOMMU page-tables allocator will release the pages when >>>>> relinquishing the domain resources. However, this is not sufficient >>>>> when the domain is dying because nothing prevents page-table to be >>>>> allocated. >>>>> >>>>> Currently page-table allocations can only happen from iommu_map(). As >>>>> the domain is dying, there is no good reason to continue to modify the >>>>> IOMMU page-tables. >>>> >>>> While I agree this to be the case right now, I'm not sure it is a >>>> good idea to build on it (in that you leave the unmap paths >>>> untouched). >>> >>> I don't build on that assumption. See next patch. >> >> Yet as said there that patch makes unmapping perhaps more fragile, >> by introducing a latent error source into the path. > > I still don't see what latent error my patch will introduce. Allocation > of page-tables are not guarantee to succeed. > > So are you implying that a code may rely on the page allocation to succeed?
I'm implying that failure to split a superpage may have unknown consequences. Since we make no use of superpages when not sharing page tables, I call this a latent issue which may go unnoticed for quite some time once no longer latent. Jan
