From: Ashish Kalra <ashish.kalra@xxxxxxx> This patch fixes issues with enabling SNP host support and effectively SNP support which is broken with respect to the KVM module being built-in. SNP host support is enabled in snp_rmptable_init() 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 enables SNP support 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) [ 10.171508] kvm_amd: Virtual VMLOAD VMSAVE supported [ 10.177052] kvm_amd: Virtual GIF supported ... ... [ 10.201648] kvm_amd: in svm_enable_virtualization_cpu 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 ... [ 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 document being referred to above: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/revision-guides/57095-PUB_1_01.pdf To summarize, 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 a #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. This patch fixes the current SNP host enabling code and effectively SNP which 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. With the AMD IOMMU driver patch applied which moves SNP enable check before enabling IOMMUs, snp_rmptable_init() can now be called early with subsys_initcall() which enables SNP host support before KVM initialization with kvm_amd module built-in. Fixes: c3b86e61b756 ("x86/cpufeatures: Enable/unmask SEV-SNP CPU feature") Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx> --- arch/x86/virt/svm/sev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c index 1dcc027ec77e..d5dc4889c445 100644 --- a/arch/x86/virt/svm/sev.c +++ b/arch/x86/virt/svm/sev.c @@ -571,7 +571,7 @@ static int __init snp_rmptable_init(void) /* * This must be called after the IOMMU has been initialized. */ -device_initcall(snp_rmptable_init); +subsys_initcall(snp_rmptable_init); static void set_rmp_segment_info(unsigned int segment_shift) { -- 2.34.1
