Merge tag 'kvm-x86-misc-6.20' of https://github.com/kvm-x86/linux into HEAD

KVM x86 misc changes for 6.20

 - Disallow changing the virtual CPU model if L2 is active, for all the same
   reasons KVM disallows change the model after the first KVM_RUN.

 - Fix a bug where KVM would incorrectly reject host accesses to PV MSRs that
   were advertised as supported to userspace when running with
   KVM_CAP_ENFORCE_PV_FEATURE_CPUID enabled.

 - Fix a bug where KVM would attempt to read protect guest state (CR3) when
   configuring an async #PF entry.

 - Fail the build if EXPORT_SYMBOL_GPL or EXPORT_SYMBOL is used in KVM (for x86
   only) to enforce usage of EXPORT_SYMBOL_FOR_KVM_INTERNAL.  Explicitly allow
   the few exports that are intended for external usage.

 - Ignore -EBUSY when checking nested events after a vCPU exits blocking as
   the WARN is user-triggerable, and because exiting to userspace on -EBUSY
   does more harm than good in pretty much every situation.

 - Throw in the towel and drop the WARN on INIT/SIPI being blocked when vCPU is
   in Wait-For-SIPI, as playing whack-a-mole with syzkaller turned out to be an
   unwinnable game.

 - Add support for new Intel instructions that don't require anything beyond
   enumerating feature flags to userspace.

 - Grab SRCU when reading PDPTRs in KVM_GET_SREGS2.

 - Add WARNs to guard against modifying KVM's CPU caps outside of the intended
   setup flow, as nested VMX in particular is sensitive to unexpected changes
   in KVM's golden configuration.

 - Add a quirk to allow userspace to opt-in to actually suppress EOI broadcasts
   when the suppression feature is enabled by the guest (currently limited to
   split IRQCHIP, i.e. userspace I/O APIC).  Sadly, simply fixing KVM to honor
   Suppress EOI Broadcasts isn't an option as some userspaces have come to rely
   on KVM's buggy behavior (KVM advertises Supress EOI Broadcast irrespective
   of whether or not userspace I/O APIC supports Directed EOIs).

 - Minor cleanups.

1 files changed, 26 insertions, 2 deletions

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 49f043246f95..095095ae01dd 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7908,8 +7908,10 @@ Will return -EBUSY if a VCPU has already been created.
 
 Valid feature flags in args[0] are::
 
-  #define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)
-  #define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK  (1ULL << 1)
+  #define KVM_X2APIC_API_USE_32BIT_IDS                          (1ULL << 0)
+  #define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK                (1ULL << 1)
+  #define KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST              (1ULL << 2)
+  #define KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST             (1ULL << 3)
 
 Enabling KVM_X2APIC_API_USE_32BIT_IDS changes the behavior of
 KVM_SET_GSI_ROUTING, KVM_SIGNAL_MSI, KVM_SET_LAPIC, and KVM_GET_LAPIC,
@@ -7922,6 +7924,28 @@ as a broadcast even in x2APIC mode in order to support physical x2APIC
 without interrupt remapping.  This is undesirable in logical mode,
 where 0xff represents CPUs 0-7 in cluster 0.
 
+Setting KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST instructs KVM to enable
+Suppress EOI Broadcasts.  KVM will advertise support for Suppress EOI
+Broadcast to the guest and suppress LAPIC EOI broadcasts when the guest
+sets the Suppress EOI Broadcast bit in the SPIV register.  This flag is
+supported only when using a split IRQCHIP.
+
+Setting KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST disables support for
+Suppress EOI Broadcasts entirely, i.e. instructs KVM to NOT advertise
+support to the guest.
+
+Modern VMMs should either enable KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST
+or KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST.  If not, legacy quirky
+behavior will be used by KVM: in split IRQCHIP mode, KVM will advertise
+support for Suppress EOI Broadcasts but not actually suppress EOI
+broadcasts; for in-kernel IRQCHIP mode, KVM will not advertise support for
+Suppress EOI Broadcasts.
+
+Setting both KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST and
+KVM_X2APIC_DISABLE_SUPPRESS_EOI_BROADCAST will fail with an EINVAL error,
+as will setting KVM_X2APIC_ENABLE_SUPPRESS_EOI_BROADCAST without a split
+IRCHIP.
+
 7.8 KVM_CAP_S390_USER_INSTR0
 ----------------------------