Commit 6be3ae45 authored by Aaron Lewis's avatar Aaron Lewis Committed by Sean Christopherson
Browse files

KVM: x86: Add a helper to handle filtering of unpermitted XCR0 features 



Add a helper, kvm_get_filtered_xcr0(), to dedup code that needs to account
for XCR0 features that require explicit opt-in on a per-process basis.  In
addition to documenting when KVM should/shouldn't consult
xstate_get_guest_group_perm(), the helper will also allow sanitizing the
filtered XCR0 to avoid enumerating architecturally illegal XCR0 values,
e.g. XTILE_CFG without XTILE_DATA.

No functional changes intended.

Signed-off-by: default avatarAaron Lewis <aaronlewis@google.com>
Reviewed-by: default avatarMingwei Zhang <mizhang@google.com>
[sean: rename helper, move to x86.h, massage changelog]
Reviewed-by: default avatarAaron Lewis <aaronlewis@google.com>
Tested-by: default avatarAaron Lewis <aaronlewis@google.com>
Link: https://lore.kernel.org/r/20230405004520.421768-2-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 77121450

arch/x86/kvm/cpuid.c

+1 −1
Original line number Diff line number Diff line
@@ -1002,7 +1002,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) 
		entry->eax = entry->ebx = entry->ecx = 0;

		break;

	case 0xd: {

		u64 permitted_xcr0 = kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();

		u64 permitted_xcr0 = kvm_get_filtered_xcr0();

		u64 permitted_xss = kvm_caps.supported_xss;



		entry->eax &= permitted_xcr0;

arch/x86/kvm/x86.c

+1 −3
Original line number Diff line number Diff line
@@ -4531,9 +4531,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
			r = 0;

		break;

	case KVM_CAP_XSAVE2: {

		u64 guest_perm = xstate_get_guest_group_perm();



		r = xstate_required_size(kvm_caps.supported_xcr0 & guest_perm, false);

		r = xstate_required_size(kvm_get_filtered_xcr0(), false);

		if (r < sizeof(struct kvm_xsave))

			r = sizeof(struct kvm_xsave);

		break;

arch/x86/kvm/x86.h

+13 −0
Original line number Diff line number Diff line
@@ -315,6 +315,19 @@ extern struct kvm_caps kvm_caps; 


extern bool enable_pmu;



/*

 * Get a filtered version of KVM's supported XCR0 that strips out dynamic

 * features for which the current process doesn't (yet) have permission to use.

 * This is intended to be used only when enumerating support to userspace,

 * e.g. in KVM_GET_SUPPORTED_CPUID and KVM_CAP_XSAVE2, it does NOT need to be

 * used to check/restrict guest behavior as KVM rejects KVM_SET_CPUID{2} if

 * userspace attempts to enable unpermitted features.

 */

static inline u64 kvm_get_filtered_xcr0(void)

{

	return kvm_caps.supported_xcr0 & xstate_get_guest_group_perm();

}



static inline bool kvm_mpx_supported(void)

{

	return (kvm_caps.supported_xcr0 & (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR))