On 2/20/23 19:38, Michael Roth wrote: > +static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned long error_code, > + unsigned long address) > +{ > + int rmp_level, level; > + pgd_t *pgd; > + pte_t *pte; > + u64 pfn; > + > + pgd = __va(read_cr3_pa()); > + pgd += pgd_index(address); > + > + pte = lookup_address_in_pgd(pgd, address, &level); > + > + /* > + * It can happen if there was a race between an unmap event and > + * the RMP fault delivery. > + */ > + if (!pte || !pte_present(*pte)) > + return RMP_PF_UNMAP; > + > + /* > + * RMP page fault handler follows this algorithm: > + * 1. Compute the pfn for the 4kb page being accessed > + * 2. Read that RMP entry -- If it is assigned then kill the process > + * 3. Otherwise, check the level from the host page table > + * If level=PG_LEVEL_4K then the page is already smashed > + * so just retry the instruction > + * 4. If level=PG_LEVEL_2M/1G, then the host page needs to be split > + */ > + > + pfn = pte_pfn(*pte); > + > + /* If its large page then calculte the fault pfn */ > + if (level > PG_LEVEL_4K) > + pfn = pfn | PFN_DOWN(address & (page_level_size(level) - 1)); > + > + /* > + * If its a guest private page, then the fault cannot be resolved. > + * Send a SIGBUS to terminate the process. > + * > + * As documented in APM vol3 pseudo-code for RMPUPDATE, when the 2M range > + * is covered by a valid (Assigned=1) 2M entry, the middle 511 4k entries > + * also have Assigned=1. This means that if there is an access to a page > + * which happens to lie within an Assigned 2M entry, the 4k RMP entry > + * will also have Assigned=1. Therefore, the kernel should see that > + * the page is not a valid page and the fault cannot be resolved. > + */ > + if (snp_lookup_rmpentry(pfn, &rmp_level)) { > + pr_info("Fatal RMP page fault, terminating process, entry assigned for pfn 0x%llx\n", > + pfn); > + do_sigbus(regs, error_code, address, VM_FAULT_SIGBUS); > + return RMP_PF_RETRY; > + } WRT my reply to 12/56, for example here it might be useful to distinguish the rmp being assigned from an error of snp_lookup_rmpentry()? > + > + /* > + * The backing page level is higher than the RMP page level, request > + * to split the page. > + */ > + if (level > rmp_level) > + return RMP_PF_SPLIT; > + > + return RMP_PF_RETRY; > +} > + > /*