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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v3 3/3] x86/vmx: implement Notify VM Exit
Under certain conditions guests can get the CPU stuck in an unbounded loop without the possibility of an interrupt window to occur on instruction boundary. This was the case with the scenarios described in XSA-156. Make use of the Notify VM Exit mechanism, that will trigger a VM Exit if no interrupt window occurs for a specified amount of time. Note that using the Notify VM Exit avoids having to trap #AC and #DB exceptions, as Xen is guaranteed to get a VM Exit even if the guest puts the CPU in a loop without an interrupt window, as such disable the intercepts if the feature is available and enabled. Setting the notify VM exit window to 0 is safe because there's a threshold added by the hardware in order to have a sane window value. Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> --- Changes since v2: - Move up the logic to set the exception bitmap in construct_vmcs(). - Change perfcounter description. Changes since v1: - Properly update debug state when using notify VM exit. - Reword commit message. --- Intel is working on getting the ISE updated to note that 0 is always a safe value to use because the hardware will add an internal threshold to assert so: https://lore.kernel.org/xen-devel/3c64db19-00fe-05bf-ac4d-6ef4201b6aa0@xxxxxxxxx/ --- docs/misc/xen-command-line.pandoc | 11 +++++++++ xen/arch/x86/hvm/vmx/vmcs.c | 17 +++++++++++++ xen/arch/x86/hvm/vmx/vmx.c | 32 +++++++++++++++++++++++-- xen/arch/x86/include/asm/hvm/vmx/vmcs.h | 4 ++++ xen/arch/x86/include/asm/hvm/vmx/vmx.h | 6 +++++ xen/arch/x86/include/asm/perfc_defn.h | 3 ++- 6 files changed, 70 insertions(+), 3 deletions(-) diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc index da18172e50..272be0e79f 100644 --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -2566,6 +2566,17 @@ guest will notify Xen that it has failed to acquire a spinlock. <major>, <minor> and <build> must be integers. The values will be encoded in guest CPUID 0x40000002 if viridian enlightenments are enabled. +### vm-notify-window (Intel) +> `= <integer>` + +> Default: `0` + +Specify the value of the VM Notify window used to detect locked VMs. Set to -1 +to disable the feature. Value is in units of crystal clock cycles. + +Note the hardware might add a threshold to the provided value in order to make +it safe, and hence using 0 is fine. + ### vpid (Intel) > `= <boolean>` diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c index d388e6729c..4985d25b85 100644 --- a/xen/arch/x86/hvm/vmx/vmcs.c +++ b/xen/arch/x86/hvm/vmx/vmcs.c @@ -67,6 +67,9 @@ integer_param("ple_gap", ple_gap); static unsigned int __read_mostly ple_window = 4096; integer_param("ple_window", ple_window); +static unsigned int __ro_after_init vm_notify_window; +integer_param("vm-notify-window", vm_notify_window); + static bool __read_mostly opt_ept_pml = true; static s8 __read_mostly opt_ept_ad = -1; int8_t __read_mostly opt_ept_exec_sp = -1; @@ -210,6 +213,7 @@ static void __init vmx_display_features(void) P(cpu_has_vmx_pml, "Page Modification Logging"); P(cpu_has_vmx_tsc_scaling, "TSC Scaling"); P(cpu_has_vmx_bus_lock_detection, "Bus Lock Detection"); + P(cpu_has_vmx_notify_vm_exiting, "Notify VM Exit"); #undef P if ( !printed ) @@ -329,6 +333,8 @@ static int vmx_init_vmcs_config(bool bsp) opt |= SECONDARY_EXEC_UNRESTRICTED_GUEST; if ( opt_ept_pml ) opt |= SECONDARY_EXEC_ENABLE_PML; + if ( vm_notify_window != ~0u ) + opt |= SECONDARY_EXEC_NOTIFY_VM_EXITING; /* * "APIC Register Virtualization" and "Virtual Interrupt Delivery" @@ -1290,6 +1296,17 @@ static int construct_vmcs(struct vcpu *v) v->arch.hvm.vmx.exception_bitmap = HVM_TRAP_MASK | (paging_mode_hap(d) ? 0 : (1U << TRAP_page_fault)) | (v->arch.fully_eager_fpu ? 0 : (1U << TRAP_no_device)); + if ( cpu_has_vmx_notify_vm_exiting ) + { + __vmwrite(NOTIFY_WINDOW, vm_notify_window); + /* + * Disable #AC and #DB interception: by using VM Notify Xen is + * guaranteed to get a VM exit even if the guest manages to lock the + * CPU. + */ + v->arch.hvm.vmx.exception_bitmap &= ~((1U << TRAP_debug) | + (1U << TRAP_alignment_check)); + } vmx_update_exception_bitmap(v); v->arch.hvm.guest_cr[0] = X86_CR0_PE | X86_CR0_ET; diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index d69c02b00a..b372cde33e 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -1419,10 +1419,19 @@ static void cf_check vmx_update_host_cr3(struct vcpu *v) void vmx_update_debug_state(struct vcpu *v) { + unsigned int mask = 1u << TRAP_int3; + + if ( !cpu_has_monitor_trap_flag && cpu_has_vmx_notify_vm_exiting ) + /* + * Only allow toggling TRAP_debug if notify VM exit is enabled, as + * unconditionally setting TRAP_debug is part of the XSA-156 fix. + */ + mask |= 1u << TRAP_debug; + if ( v->arch.hvm.debug_state_latch ) - v->arch.hvm.vmx.exception_bitmap |= 1U << TRAP_int3; + v->arch.hvm.vmx.exception_bitmap |= mask; else - v->arch.hvm.vmx.exception_bitmap &= ~(1U << TRAP_int3); + v->arch.hvm.vmx.exception_bitmap &= ~mask; vmx_vmcs_enter(v); vmx_update_exception_bitmap(v); @@ -4150,6 +4159,9 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) switch ( vector ) { case TRAP_debug: + if ( cpu_has_monitor_trap_flag && cpu_has_vmx_notify_vm_exiting ) + goto exit_and_crash; + /* * Updates DR6 where debugger can peek (See 3B 23.2.1, * Table 23-1, "Exit Qualification for Debug Exceptions"). @@ -4589,6 +4601,22 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) */ break; + case EXIT_REASON_NOTIFY: + __vmread(EXIT_QUALIFICATION, &exit_qualification); + + if ( exit_qualification & NOTIFY_VM_CONTEXT_INVALID ) + { + perfc_incr(vmnotify_crash); + gprintk(XENLOG_ERR, "invalid VM context after notify vmexit\n"); + domain_crash(v->domain); + break; + } + + if ( unlikely(exit_qualification & INTR_INFO_NMI_UNBLOCKED_BY_IRET) ) + undo_nmis_unblocked_by_iret(); + + break; + case EXIT_REASON_VMX_PREEMPTION_TIMER_EXPIRED: case EXIT_REASON_INVPCID: /* fall through */ diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h index 5d3edc1642..0961eabf3f 100644 --- a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h +++ b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h @@ -267,6 +267,7 @@ extern u32 vmx_vmentry_control; #define SECONDARY_EXEC_XSAVES 0x00100000 #define SECONDARY_EXEC_TSC_SCALING 0x02000000 #define SECONDARY_EXEC_BUS_LOCK_DETECTION 0x40000000 +#define SECONDARY_EXEC_NOTIFY_VM_EXITING 0x80000000 extern u32 vmx_secondary_exec_control; #define VMX_EPT_EXEC_ONLY_SUPPORTED 0x00000001 @@ -348,6 +349,8 @@ extern u64 vmx_ept_vpid_cap; (vmx_secondary_exec_control & SECONDARY_EXEC_TSC_SCALING) #define cpu_has_vmx_bus_lock_detection \ (vmx_secondary_exec_control & SECONDARY_EXEC_BUS_LOCK_DETECTION) +#define cpu_has_vmx_notify_vm_exiting \ + (vmx_secondary_exec_control & SECONDARY_EXEC_NOTIFY_VM_EXITING) #define VMCS_RID_TYPE_MASK 0x80000000 @@ -455,6 +458,7 @@ enum vmcs_field { SECONDARY_VM_EXEC_CONTROL = 0x0000401e, PLE_GAP = 0x00004020, PLE_WINDOW = 0x00004022, + NOTIFY_WINDOW = 0x00004024, VM_INSTRUCTION_ERROR = 0x00004400, VM_EXIT_REASON = 0x00004402, VM_EXIT_INTR_INFO = 0x00004404, diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmx.h b/xen/arch/x86/include/asm/hvm/vmx/vmx.h index bc0caad6fb..e429de8541 100644 --- a/xen/arch/x86/include/asm/hvm/vmx/vmx.h +++ b/xen/arch/x86/include/asm/hvm/vmx/vmx.h @@ -221,6 +221,7 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc) #define EXIT_REASON_XSAVES 63 #define EXIT_REASON_XRSTORS 64 #define EXIT_REASON_BUS_LOCK 74 +#define EXIT_REASON_NOTIFY 75 /* Remember to also update VMX_PERF_EXIT_REASON_SIZE! */ /* @@ -236,6 +237,11 @@ static inline void pi_clear_sn(struct pi_desc *pi_desc) #define INTR_INFO_VALID_MASK 0x80000000 /* 31 */ #define INTR_INFO_RESVD_BITS_MASK 0x7ffff000 +/* + * Exit Qualifications for NOTIFY VM EXIT + */ +#define NOTIFY_VM_CONTEXT_INVALID 1u + /* * Exit Qualifications for MOV for Control Register Access */ diff --git a/xen/arch/x86/include/asm/perfc_defn.h b/xen/arch/x86/include/asm/perfc_defn.h index d6eb661940..a710fba8a8 100644 --- a/xen/arch/x86/include/asm/perfc_defn.h +++ b/xen/arch/x86/include/asm/perfc_defn.h @@ -6,7 +6,7 @@ PERFCOUNTER_ARRAY(exceptions, "exceptions", 32) #ifdef CONFIG_HVM -#define VMX_PERF_EXIT_REASON_SIZE 75 +#define VMX_PERF_EXIT_REASON_SIZE 76 #define VMEXIT_NPF_PERFC 143 #define SVM_PERF_EXIT_REASON_SIZE (VMEXIT_NPF_PERFC + 1) PERFCOUNTER_ARRAY(vmexits, "vmexits", @@ -126,5 +126,6 @@ PERFCOUNTER(realmode_exits, "vmexits from realmode") PERFCOUNTER(pauseloop_exits, "vmexits from Pause-Loop Detection") PERFCOUNTER(buslock, "Bus Locks Detected") +PERFCOUNTER(vmnotify_crash, "domain crashes by Notify VM Exit") /*#endif*/ /* __XEN_PERFC_DEFN_H__ */ -- 2.37.0
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