On Mon, Feb 10, 2025 at 10:54:18PM +0000, Ashish Kalra wrote: > From: Ashish Kalra <ashish.kalra@xxxxxxx> > > Fix 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 > device_initcall(). SNP check on IOMMU is done during IOMMU PCI init > (IOMMU_PCI_INIT stage). And for that reason snp_rmptable_init() is > currently invoked via device_initcall() and cannot be invoked via > subsys_initcall() as core IOMMU subsystem gets initialized via > subsys_initcall(). > > 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. > > Essentially SNP host enabling code should be invoked before KVM > initialization, which is currently not the case when KVM is built-in. > > Add fix to call snp_rmptable_init() early from iommu_snp_enable() > directly and not invoked via device_initcall() which enables SNP host > support before KVM initialization with kvm_amd module built-in. > > Add additional handling for `iommu=off` or `amd_iommu=off` options. > > Note that IOMMUs need to be enabled for SNP initialization, therefore, > if host SNP support is enabled but late IOMMU initialization fails > then that will cause PSP driver's SNP_INIT to fail as IOMMU SNP sanity > checks in SNP firmware will fail with invalid configuration error as > below: > > [ 9.723114] ccp 0000:23:00.1: sev enabled > [ 9.727602] ccp 0000:23:00.1: psp enabled > [ 9.732527] ccp 0000:a2:00.1: enabling device (0000 -> 0002) > [ 9.739098] ccp 0000:a2:00.1: no command queues available > [ 9.745167] ccp 0000:a2:00.1: psp enabled > [ 9.805337] ccp 0000:23:00.1: SEV-SNP: failed to INIT rc -5, error 0x3 > [ 9.866426] ccp 0000:23:00.1: SEV API:1.53 build:5 > > Fixes: c3b86e61b756 ("x86/cpufeatures: Enable/unmask SEV-SNP CPU feature") > Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Co-developed-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Signed-off-by: Vasant Hegde <vasant.hegde@xxxxxxx> > Cc: <Stable@xxxxxxxxxxxxxxx> > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx> > --- > arch/x86/include/asm/sev.h | 2 ++ > arch/x86/virt/svm/sev.c | 23 +++++++---------------- > drivers/iommu/amd/init.c | 34 ++++++++++++++++++++++++++++++---- > 3 files changed, 39 insertions(+), 20 deletions(-) For the IOMMU part: Acked-by: Joerg Roedel <jroedel@xxxxxxx>
