Commit 1f6f68fc authored by Sean Christopherson's avatar Sean Christopherson
Browse files

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



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: default avatarBinbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: default avatarXiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-27-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 69cc3e88

arch/x86/kvm/cpuid.c

+8 −0
Original line number Diff line number Diff line
@@ -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),