On 1/13/2025 9:03 AM, Kalra, Ashish wrote: > > On 1/10/2025 6:40 PM, Sean Christopherson wrote: >> On Fri, Jan 10, 2025, Ashish Kalra wrote: >>> It looks like i have hit a serious blocker issue with this approach of moving >>> SEV/SNP initialization to KVM module load time. >>> >>> While testing with kvm_amd and PSP driver built-in, it looks like kvm_amd >>> driver is being loaded/initialized before PSP driver is loaded, and that >>> causes sev_platform_init() call from sev_hardware_setup(kvm_amd) to fail: >>> >>> [ 10.717898] kvm_amd: TSC scaling supported >>> [ 10.722470] kvm_amd: Nested Virtualization enabled >>> [ 10.727816] kvm_amd: Nested Paging enabled >>> [ 10.732388] kvm_amd: LBR virtualization supported >>> [ 10.737639] kvm_amd: SEV enabled (ASIDs 100 - 509) >>> [ 10.742985] kvm_amd: SEV-ES enabled (ASIDs 1 - 99) >>> [ 10.748333] kvm_amd: SEV-SNP enabled (ASIDs 1 - 99) >>> [ 10.753768] PSP driver not init <<<---- sev_platform_init() returns failure as PSP driver is still not initialized >>> [ 10.757563] kvm_amd: Virtual VMLOAD VMSAVE supported >>> [ 10.763124] kvm_amd: Virtual GIF supported >>> ... >>> ... >>> [ 12.514857] ccp 0000:23:00.1: enabling device (0000 -> 0002) >>> [ 12.521691] ccp 0000:23:00.1: no command queues available >>> [ 12.527991] ccp 0000:23:00.1: sev enabled >>> [ 12.532592] ccp 0000:23:00.1: psp enabled >>> [ 12.537382] ccp 0000:a2:00.1: enabling device (0000 -> 0002) >>> [ 12.544389] ccp 0000:a2:00.1: no command queues available >>> [ 12.550627] ccp 0000:a2:00.1: psp enabled >>> >>> depmod -> modules.builtin show kernel/arch/x86/kvm/kvm_amd.ko higher on the list and before kernel/drivers/crypto/ccp/ccp.ko >>> >>> modules.builtin: >>> kernel/arch/x86/kvm/kvm.ko >>> kernel/arch/x86/kvm/kvm-amd.ko >>> ... >>> ... >>> kernel/drivers/crypto/ccp/ccp.ko >>> >>> I believe that the modules which are compiled first get called first and it >>> looks like that the only way to change the order for builtin modules is by >>> changing which makefiles get compiled first ? >>> >>> Is there a way to change the load order of built-in modules and/or change >>> dependency of built-in modules ? >> >> The least awful option I know of would be to have the PSP use a higher priority >> initcall type so that it runs before the standard initcalls. When compiled as >> a module, all initcall types are #defined to module_init. >> >> E.g. this should work, /cross fingers >> >> diff --git a/drivers/crypto/ccp/sp-dev.c b/drivers/crypto/ccp/sp-dev.c >> index 7eb3e4668286..02c49fbf6198 100644 >> --- a/drivers/crypto/ccp/sp-dev.c >> +++ b/drivers/crypto/ccp/sp-dev.c >> @@ -295,5 +295,6 @@ static void __exit sp_mod_exit(void) >> #endif >> } >> >> -module_init(sp_mod_init); >> +/* The PSP needs to be initialized before dependent modules, e.g. before KVM. */ >> +subsys_initcall(sp_mod_init); >> module_exit(sp_mod_exit); > > Thanks for the suggestion, but there are actually two major issues here: > > With the above change, PSP driver initialization fails as following: > > ... > [ 7.274005] pci 0000:20:08.1: bridge window [mem 0xf6200000-0xf64fffff]: not claimed; can't enable device > [ 7.277945] pci 0000:20:08.1: Error enabling bridge (-22), continuing > [ 7.281947] ccp 0000:23:00.1: BAR 2 [mem 0xf6300000-0xf63fffff]: not claimed; can't enable device > [ 7.285945] ccp 0000:23:00.1: pcim_enable_device failed (-22) > [ 7.289943] ccp 0000:23:00.1: initialization failed > [ 7.293944] ccp 0000:23:00.1: probe with driver ccp failed with error -22 > [ 7.301981] pci 0000:a0:08.1: bridge window [mem 0xb6200000-0xb63fffff]: not claimed; can't enable device > [ 7.313956] pci 0000:a0:08.1: Error enabling bridge (-22), continuing > [ 7.321947] ccp 0000:a2:00.1: BAR 2 [mem 0xb6200000-0xb62fffff]: not claimed; can't enable device > [ 7.329945] ccp 0000:a2:00.1: pcim_enable_device failed (-22) > [ 7.337943] ccp 0000:a2:00.1: initialization failed > [ 7.341946] ccp 0000:a2:00.1: probe with driver ccp failed with error -22 > ... > > It looks as PCI bus resource allocation is still not done, hence PSP driver cannot be enabled as early as subsys_initcall, > it can be initialized probably via device_initcall(), but then that will be too late as kvm_amd would have been initialized before that. > > Additionally, it looks like that there is an issue with SNP host support being enabled with kvm_amd module being built-in: > > SNP host support is enabled in snp_rmptable_init() in arch/x86/virt/svm/sev.c, which is invoked as a device_initcall(). > Here device_initcall() is used as snp_rmptable_init() expects AMD IOMMU SNP support to be enabled prior to it and the AMD IOMMU > driver is initialized after PCI bus enumeration. > > Now, if kvm_amd module is built-in, it gets initialized before SNP host support is enabled in snp_rmptable_init() : > > [ 10.131811] kvm_amd: TSC scaling supported > [ 10.136384] kvm_amd: Nested Virtualization enabled > [ 10.141734] kvm_amd: Nested Paging enabled > [ 10.146304] kvm_amd: LBR virtualization supported > [ 10.151557] kvm_amd: SEV enabled (ASIDs 100 - 509) > [ 10.156905] kvm_amd: SEV-ES enabled (ASIDs 1 - 99) > [ 10.162256] kvm_amd: SEV-SNP enabled (ASIDs 1 - 99) > [ 10.167701] PSP driver not init > [ 10.171508] kvm_amd: Virtual VMLOAD VMSAVE supported > [ 10.177052] kvm_amd: Virtual GIF supported > ... > ... > [ 10.201648] kvm_amd: in svm_enable_virtualization_cpu WRMSR VM_HSAVE_PA non-zero > > And then svm_x86_ops->enable_virtualization_cpu() (svm_enable_virtualization_cpu) programs MSR_VM_HSAVE_PA as following: > wrmsrl(MSR_VM_HSAVE_PA, sd->save_area_pa); > > So VM_HSAVE_PA is non-zero before SNP support is enabled on all CPUs. > > snp_rmptable_init() gets invoked after svm_enable_virtualization_cpu() as following : > ... > [ 11.256138] kvm_amd: in svm_enable_virtualization_cpu WRMSR VM_HSAVE_PA non-zero > ... > [ 11.264918] SEV-SNP: in snp_rmptable_init > > This triggers a #GP exception in snp_rmptable_init() when snp_enable() is invoked to set SNP_EN in SYSCFG MSR: > > [ 11.294289] unchecked MSR access error: WRMSR to 0xc0010010 (tried to write 0x0000000003fc0000) at rIP: 0xffffffffaf5d5c28 (native_write_msr+0x8/0x30) > ... > [ 11.294404] Call Trace: > [ 11.294482] <IRQ> > [ 11.294513] ? show_stack_regs+0x26/0x30 > [ 11.294522] ? ex_handler_msr+0x10f/0x180 > [ 11.294529] ? search_extable+0x2b/0x40 > [ 11.294538] ? fixup_exception+0x2dd/0x340 > [ 11.294542] ? exc_general_protection+0x14f/0x440 > [ 11.294550] ? asm_exc_general_protection+0x2b/0x30 > [ 11.294557] ? __pfx_snp_enable+0x10/0x10 > [ 11.294567] ? native_write_msr+0x8/0x30 > [ 11.294570] ? __snp_enable+0x5d/0x70 > [ 11.294575] snp_enable+0x19/0x20 > [ 11.294578] __flush_smp_call_function_queue+0x9c/0x3a0 > [ 11.294586] generic_smp_call_function_single_interrupt+0x17/0x20 > [ 11.294589] __sysvec_call_function+0x20/0x90 > [ 11.294596] sysvec_call_function+0x80/0xb0 > [ 11.294601] </IRQ> > [ 11.294603] <TASK> > [ 11.294605] asm_sysvec_call_function+0x1f/0x30 > ... > [ 11.294631] arch_cpu_idle+0xd/0x20 > [ 11.294633] default_idle_call+0x34/0xd0 > [ 11.294636] do_idle+0x1f1/0x230 > [ 11.294643] ? complete+0x71/0x80 > [ 11.294649] cpu_startup_entry+0x30/0x40 > [ 11.294652] start_secondary+0x12d/0x160 > [ 11.294655] common_startup_64+0x13e/0x141 > [ 11.294662] </TASK> > > This #GP exception is getting triggered due to the following errata for AMD family 19h Models 10h-1Fh Processors: > > Processor may generate spurious #GP(0) Exception on WRMSR instruction: > Description: > The Processor will generate a spurious #GP(0) Exception on a WRMSR instruction if the following conditions are all met: > - the target of the WRMSR is a SYSCFG register. > - the write changes the value of SYSCFG.SNPEn from 0 to 1. > - One of the threads that share the physical core has a non-zero value in the VM_HSAVE_PA MSR. > > The suggested workaround is when enabling SNP, program VM_HSAVE_PA to 0h on both threads that share a physical core before setting SYSCFG.SNPEn > > The document being referred to above: > https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/revision-guides/57095-PUB_1_01.pdf > > Therefore, with kvm_amd module being built-in, KVM/SVM initialization happens before Host SNP is enabled and this SVM initialization > sets VM_HSAVE_PA to non-zero, which then triggers this #GP when SYSCFG.SNPEn is being set and this will subsequently cause SNP_INIT(_EX) to fail > with INVALID_CONFIG error as SYSCFG[SnpEn] is not set on all CPUs. > > So it looks like the current SNP host enabling code and effectively SNP is broken with respect to the KVM module being built-in. > > Essentially SNP host enabling code should be invoked before KVM initialization, which is currently not the case when KVM is built-in. > > Additionally, the PSP driver probably needs to be initialized at device_initcall level if it is built-in, but that is much later than KVM > module initialization, therefore, that is blocker for moving SEV/SNP initialization to KVM module load time instead of PSP module probe time. > Do note that i have verified and tested that PSP module initialization works when invoked as a device_initcall(). > As a follow-up to the above issues, i have an important question: Do we really need kvm_amd module to be built-in for SEV/SNP support ? Is there any usage case/scenario where the kvm_amd module needs to be built-in for SEV/SNP support ? If we can have a requirement that kvm_amd will always be loaded as a module (for SEV/SNP usage case), then it automatically fixes the above two issues & additionally we can continue on this approach to move SEV/SNP initialization stuff to KVM from the PSP driver. Tom and i had a discussion about it and we realized as so far no one has reported this issue of SNP support being broken with respect to kvm_amd module being built-in (from the time SNP support has gone upstream), it looks like no one is currently using kvm_amd module being built-in for SNP ? Looking for feedback/comments on the above. Thanks, Ashish
