Messages in this thread | | | Date | Thu, 17 Nov 2022 10:59:32 +0800 | Subject | Re: [Patch v3 07/14] x86/hyperv: Change vTOM handling to use standard coco mechanisms | From | Tianyu Lan <> |
| |
On 11/17/2022 2:41 AM, 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 0x40000000000 (bit 46 is set). Guest phyiscal > 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 I/O APIC to use private accesses. > > To accomplish the switch in approach, the following must be done in > 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 > > * Update cc_mkenc() and cc_mkdec() to be active for Hyper-V guests. > This makes the vTOM bit part of the protection flags. > > * 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@gmail.com/ > [2]https://lore.kernel.org/all/20211213071407.314309-1-ltykernel@gmail.com/ > > Signed-off-by: Michael Kelley<mikelley@microsoft.com> > --- > arch/x86/coco/core.c | 11 +++++++++- > arch/x86/hyperv/hv_init.c | 11 ---------- > arch/x86/hyperv/ivm.c | 45 +++++++++++++++++++++++++++++++---------- > arch/x86/include/asm/mshyperv.h | 8 ++------ > arch/x86/kernel/cpu/mshyperv.c | 15 +++++++------- > arch/x86/mm/pat/set_memory.c | 3 --- > 6 files changed, 53 insertions(+), 40 deletions(-)
Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
| |