Merge tag 'kvm-x86-misc-6.13' of https://github.com/kvm-x86/linux into HEAD

KVM x86 misc changes for 6.13

 - Clean up and optimize KVM's handling of writes to MSR_IA32_APICBASE.

 - Quirk KVM's misguided behavior of initialized certain feature MSRs to
   their maximum supported feature set, which can result in KVM creating
   invalid vCPU state.  E.g. initializing PERF_CAPABILITIES to a non-zero
   value results in the vCPU having invalid state if userspace hides PDCM
   from the guest, which can lead to save/restore failures.

 - Fix KVM's handling of non-canonical checks for vCPUs that support LA57
   to better follow the "architecture", in quotes because the actual
   behavior is poorly documented.  E.g. most MSR writes and descriptor
   table loads ignore CR4.LA57 and operate purely on whether the CPU
   supports LA57.

 - Bypass the register cache when querying CPL from kvm_sched_out(), as
   filling the cache from IRQ context is generally unsafe, and harden the
   cache accessors to try to prevent similar issues from occuring in the
   future.

 - Advertise AMD_IBPB_RET to userspace, and fix a related bug where KVM
   over-advertises SPEC_CTRL when trying to support cross-vendor VMs.

 - Minor cleanups

2 files changed, 34 insertions, 0 deletions

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index edc070c6e19b..061ec93d9ecb 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8107,6 +8107,28 @@ KVM_X86_QUIRK_SLOT_ZAP_ALL          By default, for KVM_X86_DEFAULT_VM VMs, KVM
                                     or moved memslot isn't reachable, i.e KVM
                                     _may_ invalidate only SPTEs related to the
                                     memslot.
+
+KVM_X86_QUIRK_STUFF_FEATURE_MSRS    By default, at vCPU creation, KVM sets the
+                                    vCPU's MSR_IA32_PERF_CAPABILITIES (0x345),
+                                    MSR_IA32_ARCH_CAPABILITIES (0x10a),
+                                    MSR_PLATFORM_INFO (0xce), and all VMX MSRs
+                                    (0x480..0x492) to the maximal capabilities
+                                    supported by KVM.  KVM also sets
+                                    MSR_IA32_UCODE_REV (0x8b) to an arbitrary
+                                    value (which is different for Intel vs.
+                                    AMD).  Lastly, when guest CPUID is set (by
+                                    userspace), KVM modifies select VMX MSR
+                                    fields to force consistency between guest
+                                    CPUID and L2's effective ISA.  When this
+                                    quirk is disabled, KVM zeroes the vCPU's MSR
+                                    values (with two exceptions, see below),
+                                    i.e. treats the feature MSRs like CPUID
+                                    leaves and gives userspace full control of
+                                    the vCPU model definition.  This quirk does
+                                    not affect VMX MSRs CR0/CR4_FIXED1 (0x487
+                                    and 0x489), as KVM does now allow them to
+                                    be set by userspace (KVM sets them based on
+                                    guest CPUID, for safety purposes).
 =================================== ============================================
 
 7.32 KVM_CAP_MAX_VCPU_ID
diff --git a/Documentation/virt/kvm/x86/errata.rst b/Documentation/virt/kvm/x86/errata.rst
index 4116045a8744..37c79362a48f 100644
--- a/Documentation/virt/kvm/x86/errata.rst
+++ b/Documentation/virt/kvm/x86/errata.rst
@@ -33,6 +33,18 @@ Note however that any software (e.g ``WIN87EM.DLL``) expecting these features
 to be present likely predates these CPUID feature bits, and therefore
 doesn't know to check for them anyway.
 
+``KVM_SET_VCPU_EVENTS`` issue
+-----------------------------
+
+Invalid KVM_SET_VCPU_EVENTS input with respect to error codes *may* result in
+failed VM-Entry on Intel CPUs.  Pre-CET Intel CPUs require that exception
+injection through the VMCS correctly set the "error code valid" flag, e.g.
+require the flag be set when injecting a #GP, clear when injecting a #UD,
+clear when injecting a soft exception, etc.  Intel CPUs that enumerate
+IA32_VMX_BASIC[56] as '1' relax VMX's consistency checks, and AMD CPUs have no
+restrictions whatsoever.  KVM_SET_VCPU_EVENTS doesn't sanity check the vector
+versus "has_error_code", i.e. KVM's ABI follows AMD behavior.
+
 Nested virtualization features
 ------------------------------