[PATCH v2 06/66] KVM: x86: Move CPUID 0xD.1 handling out of the index>0 loop

Sean Christopherson
2020-03-03T00:00:57Z

Mov the sub-leaf 1 handling for CPUID 0xD out of the index>0 loop so
that the loop only handles index>2. Sub-leafs 2+ have identical
semantics, whereas sub-leaf 1 is effectively a feature sub-leaf.

Moving sub-leaf 1 out of the loop does duplicate a bit of code, but
the nent/maxnent code will be consolidated in a future patch, and
duplicating the clear of ECX/EDX is arguably a good thing as the reasons
for clearing said registers are completely different.

No functional change intended.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/cpuid.c | 37 ++++++++++++++++++++++---------------
1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e5cf1e0cf84a..fc8540596386 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -653,26 +653,33 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
if (!supported)
break;

- for (idx = 1, i = 1; idx < 64; ++idx) {
+ if (*nent >= maxnent)
+ goto out;
+
+ do_host_cpuid(&entry[1], function, 1);
+ ++*nent;
+
+ entry[1].eax &= kvm_cpuid_D_1_eax_x86_features;
+ cpuid_mask(&entry[1].eax, CPUID_D_1_EAX);
+ if (entry[1].eax & (F(XSAVES)|F(XSAVEC)))
+ entry[1].ebx = xstate_required_size(supported, true);
+ else
+ entry[1].ebx = 0;
+ /* Saving XSS controlled state via XSAVES isn't supported. */
+ entry[1].ecx = 0;
+ entry[1].edx = 0;
+
+ for (idx = 2, i = 2; idx < 64; ++idx) {
u64 mask = ((u64)1 << idx);
+
if (*nent >= maxnent)
goto out;

do_host_cpuid(&entry[i], function, idx);
- if (idx == 1) {
- entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
- cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
- entry[i].ebx = 0;
- if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
- entry[i].ebx =
- xstate_required_size(supported,
- true);
- } else {
- if (entry[i].eax == 0 || !(supported & mask))
- continue;
- if (WARN_ON_ONCE(entry[i].ecx & 1))
- continue;
- }
+ if (entry[i].eax == 0 || !(supported & mask))
+ continue;
+ if (WARN_ON_ONCE(entry[i].ecx & 1))
+ continue;
entry[i].ecx = 0;
entry[i].edx = 0;
++*nent;
--
2.24.1