On Mon, Feb 10, 2025 at 10:54:18PM +0000, Ashish Kalra wrote:
From: Ashish Kalra ashish.kalra@amd.com
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/revisio...
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@google.com Signed-off-by: Sean Christopherson seanjc@google.com Co-developed-by: Vasant Hegde vasant.hegde@amd.com Signed-off-by: Vasant Hegde vasant.hegde@amd.com Cc: Stable@vger.kernel.org Signed-off-by: Ashish Kalra ashish.kalra@amd.com
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@suse.de