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KVM: x86: Disable support for Shadow Stacks if TDP is disabled

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Make TDP a hard requirement for Shadow Stacks, as there are no plans to
add Shadow Stack support to the Shadow MMU.  E.g. KVM hasn't been taught
to understand the magic Writable=0,Dirty=1 combination that is required
for Shadow Stack accesses, and so enabling Shadow Stacks when using
shadow paging will put the guest into an infinite #PF loop (KVM thinks the
shadow page tables have a valid mapping, hardware says otherwise).

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-27-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-09-19 15:32:33 -07:00
parent 69cc3e8865
commit 1f6f68fcfe
1 changed files with 8 additions and 0 deletions
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8
arch/x86/kvm/cpuid.c
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@ -955,6 +955,14 @@ void kvm_set_cpu_caps(void)
if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
kvm_cpu_cap_clear(X86_FEATURE_PKU);
/*
* Shadow Stacks aren't implemented in the Shadow MMU. Shadow Stack
* accesses require "magic" Writable=0,Dirty=1 protection, which KVM
* doesn't know how to emulate or map.
*/
if (!tdp_enabled)
kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
kvm_cpu_cap_init(CPUID_7_EDX,
F(AVX512_4VNNIW),
F(AVX512_4FMAPS),