On Wed, Mar 06, 2024 at 05:51:51PM -0800, Isaku Yamahata <isaku.yamahata@xxxxxxxxxxxxxxx> wrote: > On Wed, Mar 06, 2024 at 04:36:25PM -0800, > David Matlack <dmatlack@xxxxxxxxxx> wrote: > > > On Wed, Mar 6, 2024 at 4:31 PM David Matlack <dmatlack@xxxxxxxxxx> wrote: > > > > > > On 2024-03-01 09:28 AM, isaku.yamahata@xxxxxxxxx wrote: > > > > > > > > + if (IS_ALIGNED(mapping->base_gfn, KVM_PAGES_PER_HPAGE(PG_LEVEL_1G)) && > > > > + mapping->nr_pages >= KVM_PAGES_PER_HPAGE(PG_LEVEL_1G)) > > > > + max_level = PG_LEVEL_1G; > > > > + else if (IS_ALIGNED(mapping->base_gfn, KVM_PAGES_PER_HPAGE(PG_LEVEL_2M)) && > > > > + mapping->nr_pages >= KVM_PAGES_PER_HPAGE(PG_LEVEL_2M)) > > > > + max_level = PG_LEVEL_2M; > > > > + else > > > > + max_level = PG_LEVEL_4K; > > > > > > Is there a requirement that KVM must not map memory outside of the > > > requested region? > > > > And if so, what if the requested region is already mapped with a larger page? > > Yes. We'd like to map exact gpa range for SNP or TDX case. We don't want to map > zero at around range. For SNP or TDX, we map page to GPA, it's one time > operation. It updates measurement. > > Say, we'd like to populate GPA1 and GPA2 with initial guest memory image. And > they are within same 2M range. Map GPA1 first. If GPA2 is also mapped with zero > with 2M page, the following mapping of GPA2 fails. Even if mapping of GPA2 > succeeds, measurement may be updated when mapping GPA1. > > It's user space VMM responsibility to map GPA range only once at most for SNP or > TDX. Is this too strict requirement for default VM use case to mitigate KVM > page fault at guest boot up? If so, what about a flag like EXACT_MAPPING or > something? I'm thinking as follows. What do you think? - Allow mapping larger than requested with gmem_max_level hook: Depend on the following patch. [1] The gmem_max_level hook allows vendor-backend to determine max level. By default (for default VM or sw-protected), it allows KVM_MAX_HUGEPAGE_LEVEL mapping. TDX allows only 4KB mapping. [1] https://lore.kernel.org/kvm/20231230172351.574091-31-michael.roth@xxxxxxx/ [PATCH v11 30/35] KVM: x86: Add gmem hook for determining max NPT mapping level - Pure mapping without coco operation: As Sean suggested at [2], make KVM_MAP_MEMORY pure mapping without coco operation. In the case of TDX, the API doesn't issue TDX specific operation like TDH.PAGE.ADD() and TDH.EXTEND.MR(). We need TDX specific API. [2] https://lore.kernel.org/kvm/Ze-XW-EbT9vXaagC@xxxxxxxxxx/ - KVM_MAP_MEMORY on already mapped area potentially with large page: It succeeds. Not error. It doesn't care whether the GPA is backed by large page or not. Because the use case is pre-population before guest running, it doesn't matter if the given GPA was mapped or not, and what large page level it backs. Do you want error like -EEXIST? -- Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
