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Message-ID: <Z62iWr77bPWsZcDC@8bytes.org>
Date: Thu, 13 Feb 2025 08:42:18 +0100
From: Joerg Roedel <joro@...tes.org>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
x86@...nel.org, hpa@...or.com, thomas.lendacky@....com,
john.allen@....com, herbert@...dor.apana.org.au,
davem@...emloft.net, suravee.suthikulpanit@....com, will@...nel.org,
robin.murphy@....com, michael.roth@....com, dionnaglaze@...gle.com,
nikunj@....com, ardb@...nel.org, kevinloughlin@...gle.com,
Neeraj.Upadhyay@....com, vasant.hegde@....com,
Stable@...r.kernel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
linux-coco@...ts.linux.dev, iommu@...ts.linux.dev
Subject: Re: [PATCH v4 3/3] x86/sev: Fix broken SNP support with KVM module
built-in
On Mon, Feb 10, 2025 at 10:54:18PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....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/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@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Co-developed-by: Vasant Hegde <vasant.hegde@....com>
> Signed-off-by: Vasant Hegde <vasant.hegde@....com>
> Cc: <Stable@...r.kernel.org>
> Signed-off-by: Ashish Kalra <ashish.kalra@....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@...e.de>
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