KVM x86 fixes for 7.1-rcN

- Include the kernel's linux/mman.h in KVM selftests to ensure MADV_COLLAPSE
    is defined, as older libc versions may not provide it.
 
  - Include execinfo.h if and only if KVM selftests are building against glibc,
    and provide a test_dump_stack() for non-glibc builds.
 
  - Fudge around an RCU splat in the emegerncy reboot code that is technically
    a legitimate flaw, but in practice is a non-issue and fixing the flaw, e.g.
    by adding locking, would incur meaningful risk, i.e. do more harm than good.
 
  - Rate-limit global clock updates once again (but without delayed work), as
    KVM was subtly relying on the old rate-limiting for NPT correction to guard
    against "update storms" when running without a master clock on systems with
    overcommitted CPUs.
 
  - Fix a brown paper bag goof where KVM checked if ERAPS is "dirty" instead of
    marking it dirty when emulating INVPCID.
 
  - Flush the TLB when transitioning from xAVIC => x2AVIC to ensure the CPU TLB
    doesn't contain AVIC-tagged entries for the APIC base GPA.
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Merge tag 'kvm-x86-fixes-7.1-rc6' of https://github.com/kvm-x86/linux into HEAD

KVM x86 fixes for 7.1-rcN

 - Include the kernel's linux/mman.h in KVM selftests to ensure MADV_COLLAPSE
   is defined, as older libc versions may not provide it.

 - Include execinfo.h if and only if KVM selftests are building against glibc,
   and provide a test_dump_stack() for non-glibc builds.

 - Fudge around an RCU splat in the emegerncy reboot code that is technically
   a legitimate flaw, but in practice is a non-issue and fixing the flaw, e.g.
   by adding locking, would incur meaningful risk, i.e. do more harm than good.

 - Rate-limit global clock updates once again (but without delayed work), as
   KVM was subtly relying on the old rate-limiting for NPT correction to guard
   against "update storms" when running without a master clock on systems with
   overcommitted CPUs.

 - Fix a brown paper bag goof where KVM checked if ERAPS is "dirty" instead of
   marking it dirty when emulating INVPCID.

 - Flush the TLB when transitioning from xAVIC => x2AVIC to ensure the CPU TLB
   doesn't contain AVIC-tagged entries for the APIC base GPA.

arch/x86/include/asm/kvm_host.h

@@ -1504,6 +1504,7 @@ struct kvm_arch {
 	bool use_master_clock;
 	u64 master_kernel_ns;
 	u64 master_cycle_now;
+	struct ratelimit_state kvmclock_update_rs;
 
 #ifdef CONFIG_KVM_HYPERV
 	struct kvm_hv hyperv;

arch/x86/kvm/svm/avic.c

@@ -206,6 +206,35 @@ static void avic_activate_vmcb(struct vcpu_svm *svm)
 
 	svm_clr_intercept(svm, INTERCEPT_CR8_WRITE);
 
+	/*
+	 * Flush the TLB when enabling (x2)AVIC and when transitioning between
+	 * xAVIC and x2AVIC, as the CPU may have inserted a TLB entry for the
+	 * "wrong" mapping.
+	 *
+	 * KVM uses a per-VM "scratch" page to back the APIC memslot, because
+	 * KVM also uses per-VM page tables *and* maintains the page table (NPT
+	 * or shadow page) mappings for said memslot even if one or more vCPUs
+	 * have their local APIC hardware-disabled or are in x2APIC mode, i.e.
+	 * even if one or more vCPUs' APIC MMIO BAR is effectively disabled.
+	 *
+	 * If xAVIC is fully enabled, hardware ignores the physical address in
+	 * KVM's page tables, i.e. in the leaf SPTE for the APIC memslot, and
+	 * instead redirects the access to the AVIC backing page, i.e. to the
+	 * vCPU's virtual APIC page.  If xAVIC is not enabled (APIC is either
+	 * hardware-disabled or in x2APIC mode), then guest accesses will use
+	 * the page table mapping verbatim, i.e. will access the per-VM scratch
+	 * page, as normal memory.
+	 *
+	 * In both cases, the CPU is allowed to cache TLB entries for the APIC
+	 * base GPA.  So, KVM needs to flush the TLB when enabling xAVIC, as
+	 * accesses need to be redirected to the virtual APIC page, but the TLB
+	 * may contain entries pointing at the scratch page.  KVM also needs to
+	 * flush the TLB when enabling x2AVIC, as accesses need to go to the
+	 * scratch page, but the TLB may contain entries tagged as xAVIC, i.e.
+	 * entries pointing to the vCPU's virtual APIC page.
+	 */
+	kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu);
+
 	/*
 	 * Note: KVM supports hybrid-AVIC mode, where KVM emulates x2APIC MSR
 	 * accesses, while interrupt injection to a running vCPU can be
@@ -219,12 +248,6 @@ static void avic_activate_vmcb(struct vcpu_svm *svm)
 		/* Disabling MSR intercept for x2APIC registers */
 		avic_set_x2apic_msr_interception(svm, false);
 	} else {
-		/*
-		 * Flush the TLB, the guest may have inserted a non-APIC
-		 * mapping into the TLB while AVIC was disabled.
-		 */
-		kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu);
-
 		/* Enabling MSR intercept for x2APIC registers */
 		avic_set_x2apic_msr_interception(svm, true);
 	}

arch/x86/kvm/x86.c

@@ -5227,8 +5227,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		 * On a host with synchronized TSC, there is no need to update
 		 * kvmclock on vcpu->cpu migration
 		 */
-		if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
-			kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
+		if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) {
+			if (__ratelimit(&vcpu->kvm->arch.kvmclock_update_rs))
+				kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
+			else
+				kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+		}
+
 		if (vcpu->cpu != cpu)
 			kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu);
 		vcpu->cpu = cpu;
@@ -13366,6 +13371,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	raw_spin_lock_init(&kvm->arch.tsc_write_lock);
 	mutex_init(&kvm->arch.apic_map_lock);
 	seqcount_raw_spinlock_init(&kvm->arch.pvclock_sc, &kvm->arch.tsc_write_lock);
+	ratelimit_state_init(&kvm->arch.kvmclock_update_rs, HZ, 10);
+	ratelimit_set_flags(&kvm->arch.kvmclock_update_rs, RATELIMIT_MSG_ON_RELEASE);
 	kvm->arch.kvmclock_offset = -get_kvmclock_base_ns();
 
 	raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
@@ -14323,7 +14330,7 @@ int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva)
 		 * the RAP (Return Address Predicator).
 		 */
 		if (guest_cpu_cap_has(vcpu, X86_FEATURE_ERAPS))
-			kvm_register_is_dirty(vcpu, VCPU_EXREG_ERAPS);
+			kvm_register_mark_dirty(vcpu, VCPU_EXREG_ERAPS);
 
 		kvm_invalidate_pcid(vcpu, operand.pcid);
 		return kvm_skip_emulated_instruction(vcpu);

arch/x86/virt/hw.c

@@ -49,7 +49,20 @@ static void x86_virt_invoke_kvm_emergency_callback(void)
 {
 	cpu_emergency_virt_cb *kvm_callback;
 
-	kvm_callback = rcu_dereference(kvm_emergency_callback);
+	/*
+	 * RCU may not be watching the crashing CPU here, so rcu_dereference()
+	 * triggers a suspicious-RCU-usage splat. In principle, a concurrent
+	 * KVM module unload could race with this read; see commit 2baa33a8ddd6
+	 * ("KVM: x86: Leave user-return notifier registered on reboot/shutdown")
+	 * which notes that nothing prevents module unload during panic/reboot.
+	 *
+	 * However, taking a lock here would be riskier than the current race:
+	 * the system is going down via NMI shootdown, and any lock could be
+	 * held by an already-stopped CPU. Use rcu_dereference_raw() to silence
+	 * the lockdep splat and accept the comically small remaining race;
+	 * panic context inherently cannot guarantee complete correctness.
+	 */
+	kvm_callback = rcu_dereference_raw(kvm_emergency_callback);
 	if (kvm_callback)
 		kvm_callback();
 }

tools/testing/selftests/kvm/access_tracking_perf_test.c

@@ -41,10 +41,10 @@
 #include <inttypes.h>
 #include <limits.h>
 #include <pthread.h>
-#include <sys/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#include "kvm_syscalls.h"
 #include "kvm_util.h"
 #include "test_util.h"
 #include "memstress.h"

tools/testing/selftests/kvm/guest_memfd_test.c

@@ -14,10 +14,10 @@
 #include <linux/bitmap.h>
 #include <linux/falloc.h>
 #include <linux/sizes.h>
-#include <sys/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#include "kvm_syscalls.h"
 #include "kvm_util.h"
 #include "numaif.h"
 #include "test_util.h"

tools/testing/selftests/kvm/include/kvm_syscalls.h

@@ -2,8 +2,18 @@
 #ifndef SELFTEST_KVM_SYSCALLS_H
 #define SELFTEST_KVM_SYSCALLS_H
 
+/*
+ * Include both the kernel and libc versions of mman.h.  The kernel provides
+ * the most up-to-date flags and definitions, while libc provides the syscall
+ * wrappers tests expect.
+ */
+#include <linux/mman.h>
+
+#include <sys/mman.h>
 #include <sys/syscall.h>
 
+#include <test_util.h>
+
 #define MAP_ARGS0(m,...)
 #define MAP_ARGS1(m,t,a,...) m(t,a)
 #define MAP_ARGS2(m,t,a,...) m(t,a), MAP_ARGS1(m,__VA_ARGS__)

tools/testing/selftests/kvm/include/test_util.h

@@ -19,9 +19,9 @@
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
-#include <sys/mman.h>
 #include "kselftest.h"
 
+#include <linux/mman.h>
 #include <linux/types.h>
 
 #define msecs_to_usecs(msec)    ((msec) * 1000ULL)

tools/testing/selftests/kvm/lib/assert.c

@@ -6,11 +6,14 @@
  */
 #include "test_util.h"
 
-#include <execinfo.h>
+
 #include <sys/syscall.h>
 
 #include "kselftest.h"
 
+#ifdef __GLIBC__
+#include <execinfo.h>
+
 /* Dumps the current stack trace to stderr. */
 static void __attribute__((noinline)) test_dump_stack(void);
 static void test_dump_stack(void)
@@ -57,6 +60,9 @@ static void test_dump_stack(void)
 	system(cmd);
 #pragma GCC diagnostic pop
 }
+#else
+static void test_dump_stack(void) {}
+#endif
 
 static pid_t _gettid(void)
 {

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -5,13 +5,13 @@
  * Copyright (C) 2018, Google LLC.
  */
 #include "test_util.h"
+#include "kvm_syscalls.h"
 #include "kvm_util.h"
 #include "processor.h"
 #include "ucall_common.h"
 
 #include <assert.h>
 #include <sched.h>
-#include <sys/mman.h>
 #include <sys/resource.h>
 #include <sys/types.h>
 #include <sys/stat.h>

tools/testing/selftests/kvm/memslot_perf_test.c

@@ -15,7 +15,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/mman.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -23,6 +22,7 @@
 #include <linux/sizes.h>
 
 #include <test_util.h>
+#include <kvm_syscalls.h>
 #include <kvm_util.h>
 #include <processor.h>
 #include <ucall_common.h>

tools/testing/selftests/kvm/s390/shared_zeropage_test.c

@@ -4,11 +4,10 @@
  *
  * Copyright (C) 2024, Red Hat, Inc.
  */
-#include <sys/mman.h>
-
 #include <linux/fs.h>
 
 #include "test_util.h"
+#include "kvm_syscalls.h"
 #include "kvm_util.h"
 #include "kselftest.h"
 #include "ucall_common.h"

tools/testing/selftests/kvm/s390/tprot.c

@@ -4,8 +4,8 @@
  *
  * Copyright IBM Corp. 2021
  */
-#include <sys/mman.h>
 #include "test_util.h"
+#include "kvm_syscalls.h"
 #include "kvm_util.h"
 #include "kselftest.h"
 #include "ucall_common.h"

tools/testing/selftests/kvm/set_memory_region_test.c

@@ -8,11 +8,11 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
-#include <sys/mman.h>
 
 #include <linux/compiler.h>
 
 #include <test_util.h>
+#include <kvm_syscalls.h>
 #include <kvm_util.h>
 #include <processor.h>