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Subject[PATCH v2 08/66] KVM: x86: Warn on zero-size save state for valid CPUID 0xD.N sub-leaf
Date
WARN if the save state size for a valid XCR0-managed sub-leaf is zero,
which would indicate a KVM or CPU bug. Add a comment to explain why KVM
WARNs so the reader doesn't have to tease out the relevant bits from
Intel's SDM and KVM's XCR0/XSS code.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/cpuid.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index fd9b29aa7abc..424dde41cb5d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -677,10 +677,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
goto out;

do_host_cpuid(&entry[i], function, idx);
- if (entry[i].eax == 0)
- continue;
- if (WARN_ON_ONCE(entry[i].ecx & 1))
+
+ /*
+ * The @supported check above should have filtered out
+ * invalid sub-leafs as well as sub-leafs managed by
+ * IA32_XSS MSR. Only XCR0-managed sub-leafs should
+ * reach this point, and they should have a non-zero
+ * save state size.
+ */
+ if (WARN_ON_ONCE(!entry[i].eax || (entry[i].ecx & 1)))
continue;
+
entry[i].ecx = 0;
entry[i].edx = 0;
++*nent;
--
2.24.1
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