From: Dave Hansen <dave.hansen@xxxxxxxxx> Sent: Friday, November 11, 2022 4:22 PM > > On 11/10/22 22:21, Michael Kelley wrote: > > * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot > > * bits, just like normal ioremap(): > > */ > > - flags = pgprot_decrypted(flags); > > + if (!cc_platform_has(CC_ATTR_HAS_PARAVISOR)) > > + flags = pgprot_decrypted(flags); > > This begs the question whether *all* paravisors will want to avoid a > decrypted ioapic mapping. Is this _fundamental_ to paravisors, or it is > an implementation detail of this _individual_ paravisor? Hard to say. The paravisor that Hyper-V provides for use with the vTOM option in a SEV SNP VM is the only paravisor I've seen. At least as defined by Hyper-V and AMD SNP Virtual Machine Privilege Levels (VMPLs), the paravisor resides within the VM trust boundary. Anything that a paravisor emulates would be in the "private" (i.e., encrypted) memory so it can be accessed by both the guest OS and the paravisor. But nothing fundamental says that IOAPIC emulation *must* be done in the paravisor. I originally though about naming this attribute HAS_EMULATED_IOAPIC, but that felt a bit narrow as other emulated hardware might need similar treatment in the future, at least with the Hyper-V and AMD SEV SNP vTOM paravisor. Net, we currently have N=1 for paravisors, and we won't know what the more generalized case looks like until N >= 2. If/when that happens, additional logic might be needed here, and the name of this attribute might need adjustment to support broader usage. But if there's consensus on a different name now, or on the narrower HAS_EMULATED_IOAPIC name, it doesn’t really matter to me. Michael
