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Per the APM [1]:
Some processors, identified by CPUID Fn8000_0008_EBX[IbrsSameMode]
(bit 19) = 1, provide additional speculation limits. For these
processors, when IBRS is set, indirect branch predictions are not
influenced by any prior indirect branches, regardless of mode (CPL
and guest/host) and regardless of whether the prior indirect branches
occurred before or after the setting of IBRS. This is referred to as
Same Mode IBRS.
Define this feature bit, which will be used by KVM to determine if an
IBPB is required on nested VM-exits in SVM.
[1] AMD64 Architecture Programmer's Manual Pub. 40332, Rev 4.08 - April
2024, Volume 2, 3.2.9 Speculation Control MSRs
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20250221163352.3818347-2-yosry.ahmed@linux.dev
Signed-off-by: Sean Christopherson <seanjc@google.com>