[RFC PATCH 10/14] KVM: VMX: Move VMX enable and disable into VAC

Anish Ghulati
2023-11-07T20:21:29Z

Move loaded_vmcss_on_cpu into VAC. loaded_vmcss_on_cpu is a list of
VMCSs that have been loaded on a CPU; when offlining or kexec/crashing,
this needs to be VMCLEAR'd.

Register and unregister callbacks for vmx_emergency_disable in
vac_vmx_init/exit. These are init and exit functions for the VMX portion
of VAC. Temporarily call init and exit from vmx_init and __vmx_exit.
This will change once VAC is a module (the init/exit will be called via
module init and exit functions).

Move the call to hv_reset_evmcs from vmx_hardware_disable to
vmx_module_exit. This is because vmx_hardware_enable/disable is now part
of VAC.

Signed-off-by: Anish Ghulati <aghulati@google.com>
---
arch/x86/kvm/vac.h | 14 +++
arch/x86/kvm/vmx/vac.c | 190 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/vac.h | 7 +-
arch/x86/kvm/vmx/vmx.c | 182 ++-------------------------------------
4 files changed, 219 insertions(+), 174 deletions(-)

diff --git a/arch/x86/kvm/vac.h b/arch/x86/kvm/vac.h
index 135d3be5461e..59cbf36ff8ce 100644
--- a/arch/x86/kvm/vac.h
+++ b/arch/x86/kvm/vac.h
@@ -5,6 +5,20 @@

#include <linux/user-return-notifier.h>

+int __init vac_init(void);
+void vac_exit(void);
+
+#ifdef CONFIG_KVM_INTEL
+int __init vac_vmx_init(void);
+void vac_vmx_exit(void);
+#else
+int __init vac_vmx_init(void)
+{
+ return 0;
+}
+void vac_vmx_exit(void) {}
+#endif
+
/*
* Restoring the host value for MSRs that are only consumed when running in
* usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
diff --git a/arch/x86/kvm/vmx/vac.c b/arch/x86/kvm/vmx/vac.c
index 7b8ade0fb97f..202686ccbaec 100644
--- a/arch/x86/kvm/vmx/vac.c
+++ b/arch/x86/kvm/vmx/vac.c
@@ -1,10 +1,18 @@
// SPDX-License-Identifier: GPL-2.0-only

#include <asm/percpu.h>
+#include <asm/reboot.h>
#include <linux/percpu-defs.h>

#include "vac.h"
+#include "vmx_ops.h"
+#include "posted_intr.h"

+/*
+ * We maintain a per-CPU linked-list of VMCS loaded on that CPU. This is needed
+ * when a CPU is brought down, and we need to VMCLEAR all VMCSs loaded on it.
+ */
+static DEFINE_PER_CPU(struct list_head, loaded_vmcss_on_cpu);

static DEFINE_PER_CPU(struct vmcs *, vmxarea);

@@ -47,3 +55,185 @@ void free_vpid(int vpid)
__clear_bit(vpid, vmx_vpid_bitmap);
spin_unlock(&vmx_vpid_lock);
}
+
+void add_vmcs_to_loaded_vmcss_on_cpu(
+ struct list_head *loaded_vmcss_on_cpu_link,
+ int cpu)
+{
+ list_add(loaded_vmcss_on_cpu_link, &per_cpu(loaded_vmcss_on_cpu, cpu));
+}
+
+static void __loaded_vmcs_clear(void *arg)
+{
+ struct loaded_vmcs *loaded_vmcs = arg;
+ int cpu = raw_smp_processor_id();
+
+ if (loaded_vmcs->cpu != cpu)
+ return; /* vcpu migration can race with cpu offline */
+ if (per_cpu(current_vmcs, cpu) == loaded_vmcs->vmcs)
+ per_cpu(current_vmcs, cpu) = NULL;
+
+ vmcs_clear(loaded_vmcs->vmcs);
+ if (loaded_vmcs->shadow_vmcs && loaded_vmcs->launched)
+ vmcs_clear(loaded_vmcs->shadow_vmcs);
+
+ list_del(&loaded_vmcs->loaded_vmcss_on_cpu_link);
+
+ /*
+ * Ensure all writes to loaded_vmcs, including deleting it from its
+ * current percpu list, complete before setting loaded_vmcs->cpu to
+ * -1, otherwise a different cpu can see loaded_vmcs->cpu == -1 first
+ * and add loaded_vmcs to its percpu list before it's deleted from this
+ * cpu's list. Pairs with the smp_rmb() in vmx_vcpu_load_vmcs().
+ */
+ smp_wmb();
+
+ loaded_vmcs->cpu = -1;
+ loaded_vmcs->launched = 0;
+}
+
+void loaded_vmcs_clear(struct loaded_vmcs *loaded_vmcs)
+{
+ int cpu = loaded_vmcs->cpu;
+
+ if (cpu != -1)
+ smp_call_function_single(cpu,
+ __loaded_vmcs_clear, loaded_vmcs, 1);
+
+}
+
+static int kvm_cpu_vmxon(u64 vmxon_pointer)
+{
+ u64 msr;
+
+ cr4_set_bits(X86_CR4_VMXE);
+
+ asm_volatile_goto("1: vmxon %[vmxon_pointer]\n\t"
+ _ASM_EXTABLE(1b, %l[fault])
+ : : [vmxon_pointer] "m"(vmxon_pointer)
+ : : fault);
+ return 0;
+
+fault:
+ WARN_ONCE(1, "VMXON faulted, MSR_IA32_FEAT_CTL (0x3a) = 0x%llx\n",
+ rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr) ? 0xdeadbeef : msr);
+ cr4_clear_bits(X86_CR4_VMXE);
+
+ return -EFAULT;
+}
+
+int vmx_hardware_enable(void)
+{
+ int cpu = raw_smp_processor_id();
+ u64 phys_addr = __pa(vac_get_vmxarea(cpu));
+ int r;
+
+ if (cr4_read_shadow() & X86_CR4_VMXE)
+ return -EBUSY;
+
+ /*
+ * This can happen if we hot-added a CPU but failed to allocate
+ * VP assist page for it.
+ */
+ if (kvm_is_using_evmcs() && !hv_get_vp_assist_page(cpu))
+ return -EFAULT;
+
+ intel_pt_handle_vmx(1);
+
+ r = kvm_cpu_vmxon(phys_addr);
+ if (r) {
+ intel_pt_handle_vmx(0);
+ return r;
+ }
+
+ if (enable_ept)
+ ept_sync_global();
+
+ return 0;
+}
+
+static void vmclear_local_loaded_vmcss(void)
+{
+ int cpu = raw_smp_processor_id();
+ struct loaded_vmcs *v, *n;
+
+ list_for_each_entry_safe(v, n, &per_cpu(loaded_vmcss_on_cpu, cpu),
+ loaded_vmcss_on_cpu_link)
+ __loaded_vmcs_clear(v);
+}
+
+/*
+ * Disable VMX and clear CR4.VMXE (even if VMXOFF faults)
+ *
+ * Note, VMXOFF causes a #UD if the CPU is !post-VMXON, but it's impossible to
+ * atomically track post-VMXON state, e.g. this may be called in NMI context.
+ * Eat all faults as all other faults on VMXOFF faults are mode related, i.e.
+ * faults are guaranteed to be due to the !post-VMXON check unless the CPU is
+ * magically in RM, VM86, compat mode, or at CPL>0.
+ */
+static int kvm_cpu_vmxoff(void)
+{
+ asm_volatile_goto("1: vmxoff\n\t"
+ _ASM_EXTABLE(1b, %l[fault])
+ ::: "cc", "memory" : fault);
+
+ cr4_clear_bits(X86_CR4_VMXE);
+ return 0;
+
+fault:
+ cr4_clear_bits(X86_CR4_VMXE);
+ return -EIO;
+}
+
+static void vmx_emergency_disable(void)
+{
+ int cpu = raw_smp_processor_id();
+ struct loaded_vmcs *v;
+
+ kvm_rebooting = true;
+
+ /*
+ * Note, CR4.VMXE can be _cleared_ in NMI context, but it can only be
+ * set in task context. If this races with VMX is disabled by an NMI,
+ * VMCLEAR and VMXOFF may #UD, but KVM will eat those faults due to
+ * kvm_rebooting set.
+ */
+ if (!(__read_cr4() & X86_CR4_VMXE))
+ return;
+
+ list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
+ loaded_vmcss_on_cpu_link)
+ vmcs_clear(v->vmcs);
+
+ kvm_cpu_vmxoff();
+}
+
+void vmx_hardware_disable(void)
+{
+ vmclear_local_loaded_vmcss();
+
+ if (kvm_cpu_vmxoff())
+ kvm_spurious_fault();
+
+ intel_pt_handle_vmx(0);
+}
+
+int __init vac_vmx_init(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
+
+ pi_init_cpu(cpu);
+ }
+
+ cpu_emergency_register_virt_callback(vmx_emergency_disable);
+
+ return 0;
+}
+
+void vac_vmx_exit(void)
+{
+ cpu_emergency_unregister_virt_callback(vmx_emergency_disable);
+}
diff --git a/arch/x86/kvm/vmx/vac.h b/arch/x86/kvm/vmx/vac.h
index 46c54fe7447d..daeea8ef0d33 100644
--- a/arch/x86/kvm/vmx/vac.h
+++ b/arch/x86/kvm/vmx/vac.h
@@ -9,4 +9,9 @@ void vac_set_vmxarea(struct vmcs *vmcs, int cpu);

struct vmcs *vac_get_vmxarea(int cpu);
int allocate_vpid(void);
-void free_vpid(int vpid);
+void add_vmcs_to_loaded_vmcss_on_cpu(
+ struct list_head *loaded_vmcss_on_cpu_link,
+ int cpu);
+void loaded_vmcs_clear(struct loaded_vmcs *loaded_vmcs);
+int vmx_hardware_enable(void);
+void vmx_hardware_disable(void);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 407e37810419..46e2d5c69d1d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -456,12 +456,6 @@ noinline void invept_error(unsigned long ext, u64 eptp, gpa_t gpa)
ext, eptp, gpa);
}

-/*
- * We maintain a per-CPU linked-list of VMCS loaded on that CPU. This is needed
- * when a CPU is brought down, and we need to VMCLEAR all VMCSs loaded on it.
- */
-static DEFINE_PER_CPU(struct list_head, loaded_vmcss_on_cpu);
-
struct vmcs_config vmcs_config __ro_after_init;
struct vmx_capability vmx_capability __ro_after_init;

@@ -716,90 +710,6 @@ static int vmx_set_guest_uret_msr(struct vcpu_vmx *vmx,
return ret;
}

-/*
- * Disable VMX and clear CR4.VMXE (even if VMXOFF faults)
- *
- * Note, VMXOFF causes a #UD if the CPU is !post-VMXON, but it's impossible to
- * atomically track post-VMXON state, e.g. this may be called in NMI context.
- * Eat all faults as all other faults on VMXOFF faults are mode related, i.e.
- * faults are guaranteed to be due to the !post-VMXON check unless the CPU is
- * magically in RM, VM86, compat mode, or at CPL>0.
- */
-static int kvm_cpu_vmxoff(void)
-{
- asm_volatile_goto("1: vmxoff\n\t"
- _ASM_EXTABLE(1b, %l[fault])
- ::: "cc", "memory" : fault);
-
- cr4_clear_bits(X86_CR4_VMXE);
- return 0;
-
-fault:
- cr4_clear_bits(X86_CR4_VMXE);
- return -EIO;
-}
-
-static void vmx_emergency_disable(void)
-{
- int cpu = raw_smp_processor_id();
- struct loaded_vmcs *v;
-
- kvm_rebooting = true;
-
- /*
- * Note, CR4.VMXE can be _cleared_ in NMI context, but it can only be
- * set in task context. If this races with VMX is disabled by an NMI,
- * VMCLEAR and VMXOFF may #UD, but KVM will eat those faults due to
- * kvm_rebooting set.
- */
- if (!(__read_cr4() & X86_CR4_VMXE))
- return;
-
- list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
- loaded_vmcss_on_cpu_link)
- vmcs_clear(v->vmcs);
-
- kvm_cpu_vmxoff();
-}
-
-static void __loaded_vmcs_clear(void *arg)
-{
- struct loaded_vmcs *loaded_vmcs = arg;
- int cpu = raw_smp_processor_id();
-
- if (loaded_vmcs->cpu != cpu)
- return; /* vcpu migration can race with cpu offline */
- if (per_cpu(current_vmcs, cpu) == loaded_vmcs->vmcs)
- per_cpu(current_vmcs, cpu) = NULL;
-
- vmcs_clear(loaded_vmcs->vmcs);
- if (loaded_vmcs->shadow_vmcs && loaded_vmcs->launched)
- vmcs_clear(loaded_vmcs->shadow_vmcs);
-
- list_del(&loaded_vmcs->loaded_vmcss_on_cpu_link);
-
- /*
- * Ensure all writes to loaded_vmcs, including deleting it from its
- * current percpu list, complete before setting loaded_vmcs->cpu to
- * -1, otherwise a different cpu can see loaded_vmcs->cpu == -1 first
- * and add loaded_vmcs to its percpu list before it's deleted from this
- * cpu's list. Pairs with the smp_rmb() in vmx_vcpu_load_vmcs().
- */
- smp_wmb();
-
- loaded_vmcs->cpu = -1;
- loaded_vmcs->launched = 0;
-}
-
-void loaded_vmcs_clear(struct loaded_vmcs *loaded_vmcs)
-{
- int cpu = loaded_vmcs->cpu;
-
- if (cpu != -1)
- smp_call_function_single(cpu,
- __loaded_vmcs_clear, loaded_vmcs, 1);
-}
-
static bool vmx_segment_cache_test_set(struct vcpu_vmx *vmx, unsigned seg,
unsigned field)
{
@@ -1411,8 +1321,9 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
*/
smp_rmb();

- list_add(&vmx->loaded_vmcs->loaded_vmcss_on_cpu_link,
- &per_cpu(loaded_vmcss_on_cpu, cpu));
+ add_vmcs_to_loaded_vmcss_on_cpu(
+ &vmx->loaded_vmcs->loaded_vmcss_on_cpu_link,
+ cpu);
local_irq_enable();
}

@@ -2765,78 +2676,6 @@ static int vmx_check_processor_compat(void)
return 0;
}

-static int kvm_cpu_vmxon(u64 vmxon_pointer)
-{
- u64 msr;
-
- cr4_set_bits(X86_CR4_VMXE);
-
- asm_volatile_goto("1: vmxon %[vmxon_pointer]\n\t"
- _ASM_EXTABLE(1b, %l[fault])
- : : [vmxon_pointer] "m"(vmxon_pointer)
- : : fault);
- return 0;
-
-fault:
- WARN_ONCE(1, "VMXON faulted, MSR_IA32_FEAT_CTL (0x3a) = 0x%llx\n",
- rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr) ? 0xdeadbeef : msr);
- cr4_clear_bits(X86_CR4_VMXE);
-
- return -EFAULT;
-}
-
-static int vmx_hardware_enable(void)
-{
- int cpu = raw_smp_processor_id();
- u64 phys_addr = __pa(vac_get_vmxarea(cpu));
- int r;
-
- if (cr4_read_shadow() & X86_CR4_VMXE)
- return -EBUSY;
-
- /*
- * This can happen if we hot-added a CPU but failed to allocate
- * VP assist page for it.
- */
- if (kvm_is_using_evmcs() && !hv_get_vp_assist_page(cpu))
- return -EFAULT;
-
- intel_pt_handle_vmx(1);
-
- r = kvm_cpu_vmxon(phys_addr);
- if (r) {
- intel_pt_handle_vmx(0);
- return r;
- }
-
- if (enable_ept)
- ept_sync_global();
-
- return 0;
-}
-
-static void vmclear_local_loaded_vmcss(void)
-{
- int cpu = raw_smp_processor_id();
- struct loaded_vmcs *v, *n;
-
- list_for_each_entry_safe(v, n, &per_cpu(loaded_vmcss_on_cpu, cpu),
- loaded_vmcss_on_cpu_link)
- __loaded_vmcs_clear(v);
-}
-
-static void vmx_hardware_disable(void)
-{
- vmclear_local_loaded_vmcss();
-
- if (kvm_cpu_vmxoff())
- kvm_spurious_fault();
-
- hv_reset_evmcs();
-
- intel_pt_handle_vmx(0);
-}
-
struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags)
{
int node = cpu_to_node(cpu);
@@ -8182,13 +8021,15 @@ static void __vmx_exit(void)
{
allow_smaller_maxphyaddr = false;

- cpu_emergency_unregister_virt_callback(vmx_emergency_disable);
+ //TODO: Remove this exit call once VAC is a module
+ vac_vmx_exit();

vmx_cleanup_l1d_flush();
}

void vmx_module_exit(void)
{
+ hv_reset_evmcs();
__vmx_exit();
}

@@ -8603,7 +8444,7 @@ static struct kvm_x86_init_ops vmx_init_ops __initdata = {

int __init vmx_init(void)
{
- int r, cpu;
+ int r;

/*
* Note, hv_init_evmcs() touches only VMX knobs, i.e. there's nothing
@@ -8626,13 +8467,8 @@ int __init vmx_init(void)
if (r)
goto err_l1d_flush;

- for_each_possible_cpu(cpu) {
- INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
-
- pi_init_cpu(cpu);
- }
-
- cpu_emergency_register_virt_callback(vmx_emergency_disable);
+ //TODO: Remove this init call once VAC is a module
+ vac_vmx_init();

vmx_check_vmcs12_offsets();

--
2.42.0.869.gea05f2083d-goog