On Thu, Dec 01, 2022 at 07:30:24PM -0800, Michael Kelley wrote: > Hyper-V guests on AMD SEV-SNP hardware have the option of using the > "virtual Top Of Memory" (vTOM) feature specified by the SEV-SNP > architecture. With vTOM, shared vs. private memory accesses are > controlled by splitting the guest physical address space into two > halves. vTOM is the dividing line where the uppermost bit of the > physical address space is set; e.g., with 47 bits of guest physical > address space, vTOM is 0x400000000000 (bit 46 is set). Guest physical > memory is accessible at two parallel physical addresses -- one below > vTOM and one above vTOM. Accesses below vTOM are private (encrypted) > while accesses above vTOM are shared (decrypted). In this sense, vTOM > is like the GPA.SHARED bit in Intel TDX. > > Support for Hyper-V guests using vTOM was added to the Linux kernel in > two patch sets[1][2]. This support treats the vTOM bit as part of > the physical address. For accessing shared (decrypted) memory, these > patch sets create a second kernel virtual mapping that maps to physical > addresses above vTOM. > > A better approach is to treat the vTOM bit as a protection flag, not > as part of the physical address. This new approach is like the approach > for the GPA.SHARED bit in Intel TDX. Rather than creating a second kernel > virtual mapping, the existing mapping is updated using recently added > coco mechanisms. When memory is changed between private and shared using > set_memory_decrypted() and set_memory_encrypted(), the PTEs for the > existing kernel mapping are changed to add or remove the vTOM bit > in the guest physical address, just as with TDX. The hypercalls to > change the memory status on the host side are made using the existing > callback mechanism. Everything just works, with a minor tweak to map > the IO-APIC to use private accesses. > > To accomplish the switch in approach, the following must be done in > this single patch: s/in this single patch// > * Update Hyper-V initialization to set the cc_mask based on vTOM > and do other coco initialization. > > * Update physical_mask so the vTOM bit is no longer treated as part > of the physical address > > * Remove CC_VENDOR_HYPERV and merge the associated vTOM functionality > under CC_VENDOR_AMD. Update cc_mkenc() and cc_mkdec() to set/clear > the vTOM bit as a protection flag. > > * Code already exists to make hypercalls to inform Hyper-V about pages > changing between shared and private. Update this code to run as a > callback from __set_memory_enc_pgtable(). > > * Remove the Hyper-V special case from __set_memory_enc_dec() > > * Remove the Hyper-V specific call to swiotlb_update_mem_attributes() > since mem_encrypt_init() will now do it. > > [1] https://lore.kernel.org/all/20211025122116.264793-1-ltykernel@xxxxxxxxx/ > [2] https://lore.kernel.org/all/20211213071407.314309-1-ltykernel@xxxxxxxxx/ > > Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> > --- > arch/x86/coco/core.c | 37 ++++++++++++++++++++-------- > arch/x86/hyperv/hv_init.c | 11 --------- > arch/x86/hyperv/ivm.c | 52 +++++++++++++++++++++++++++++++--------- > arch/x86/include/asm/coco.h | 1 - > arch/x86/include/asm/mshyperv.h | 8 ++----- > arch/x86/include/asm/msr-index.h | 1 + > arch/x86/kernel/cpu/mshyperv.c | 15 ++++++------ > arch/x86/mm/pat/set_memory.c | 3 --- > 8 files changed, 78 insertions(+), 50 deletions(-) > > diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c > index 49b44f8..c361c52 100644 > --- a/arch/x86/coco/core.c > +++ b/arch/x86/coco/core.c > @@ -44,6 +44,24 @@ static bool intel_cc_platform_has(enum cc_attr attr) > static bool amd_cc_platform_has(enum cc_attr attr) > { > #ifdef CONFIG_AMD_MEM_ENCRYPT > + > + /* > + * Handle the SEV-SNP vTOM case where sme_me_mask must be zero, > + * and the other levels of SME/SEV functionality, including C-bit > + * based SEV-SNP, must not be enabled. > + */ > + if (sev_status & MSR_AMD64_SNP_VTOM_ENABLED) { return amd_cc_platform_vtom(); or so and then stick that switch in there. This way it looks kinda grafted in front and with a function call with a telling name it says it is a special case... > + switch (attr) { > + case CC_ATTR_GUEST_MEM_ENCRYPT: > + case CC_ATTR_MEM_ENCRYPT: > + case CC_ATTR_ACCESS_IOAPIC_ENCRYPTED: > + return true; > + default: > + return false; > + } > + } The rest looks kinda nice, I gotta say. I can't complain. :) Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
