On Fri, Apr 30, 2021 at 07:37:53AM -0500, Brijesh Singh wrote: > This poses a challenge in the Linux memory model. The Linux kernel > creates a direct mapping of all the physical memory -- referred to as > the physmap. The physmap may contain a valid mapping of guest owned pages. > During the page table walk, the host access may get into the situation where > one of the pages within the large page is owned by the guest (i.e assigned > bit is set in RMP). A write to a non-guest within the large page will > raise an RMP violation. To workaround it, call set_memory_4k() to split > the physmap before adding the page in the RMP table. This ensures that the > pages added in the RMP table are used as 4K in the physmap. What's an RMP violation and why are they a problem? > The spliting of the physmap is a temporary solution until the kernel page > fault handler is improved to split the kernel address on demand. How is that an improvement? Fracturing the physmap sucks whichever way around. > One of the > disadvtange of splitting is that eventually, it will end up breaking down > the entire physmap unless its coalesce back to a large page. I am open to > the suggestation on various approaches we could take to address this problem. Have the hardware fracture the TLB entry internally?
