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Index: sys/amd64/amd64/exception.S
===================================================================
--- sys/amd64/amd64/exception.S
+++ sys/amd64/amd64/exception.S
@@ -864,7 +864,10 @@
movl %edx,%eax
shrq $32,%rdx
wrmsr
- movq %r13,%cr3
+ cmpb $0, nmi_flush_l1d_sw(%rip)
+ je 2f
+ call flush_l1d_sw /* bhyve L1TF assist */
+2: movq %r13,%cr3
RESTORE_REGS
addq $TF_RIP,%rsp
jmp doreti_iret
Index: sys/amd64/amd64/support.S
===================================================================
--- sys/amd64/amd64/support.S
+++ sys/amd64/amd64/support.S
@@ -1225,3 +1225,36 @@
END(handle_ibrs_exit_rs)
.noaltmacro
+
+/*
+ * Flush L1D cache. Load enough of the data from the kernel text
+ * to flush existing L1D content.
+ *
+ * N.B. The function follows ABI calling conventions, but the vmm.ko
+ * caller expects that only %rax, %rcx, %r9, and %rflags registers
+ * are clobbered.
+ */
+ENTRY(flush_l1d_sw)
+#define L1D_FLUSH_SIZE (64 * 1024)
+ movq $KERNBASE, %r9
+ movq $-L1D_FLUSH_SIZE, %rcx
+ /*
+ * pass 1: Preload TLB.
+ * Kernel text is mapped using superpages. TLB preload is
+ * done for the benefit of older CPUs which split 2M page
+ * into 4k TLB entries.
+ */
+1: movb L1D_FLUSH_SIZE(%r9, %rcx), %al
+ addq $PAGE_SIZE, %rcx
+ jne 1b
+ xorl %eax, %eax
+ cpuid
+ movq $-L1D_FLUSH_SIZE, %rcx
+ /* pass 2: Read each cache line. */
+2: movb L1D_FLUSH_SIZE(%r9, %rcx), %al
+ addq $64, %rcx
+ jne 2b
+ lfence
+ ret
+#undef L1D_FLUSH_SIZE
+END(flush_l1d_sw)
Index: sys/amd64/amd64/trap.c
===================================================================
--- sys/amd64/amd64/trap.c
+++ sys/amd64/amd64/trap.c
@@ -160,6 +160,20 @@
&uprintf_signal, 0,
"Print debugging information on trap signal to ctty");
+/*
+ * Control L1D flush on return from NMI.
+ *
+ * Tunable can be set to the following values:
+ * 0 - only enable flush on return from NMI if required by vmm.ko (default)
+ * >1 - always flush on return from NMI.
+ *
+ * Post-boot, the sysctl indicates if flushing is currently enabled.
+ */
+int nmi_flush_l1d_sw;
+SYSCTL_INT(_machdep, OID_AUTO, nmi_flush_l1d_sw, CTLFLAG_RWTUN,
+ &nmi_flush_l1d_sw, 0,
+ "Flush L1 Data Cache on NMI exit, software bhyve L1TF mitigation assist");
+
/*
* Exception, fault, and trap interface to the FreeBSD kernel.
* This common code is called from assembly language IDT gate entry
Index: sys/amd64/include/md_var.h
===================================================================
--- sys/amd64/include/md_var.h
+++ sys/amd64/include/md_var.h
@@ -40,6 +40,7 @@
extern int hw_lower_amd64_sharedpage;
extern int hw_ibrs_disable;
extern int hw_ssb_disable;
+extern int nmi_flush_l1d_sw;
/*
* The file "conf/ldscript.amd64" defines the symbol "kernphys". Its
Index: sys/amd64/vmm/intel/vmx.c
===================================================================
--- sys/amd64/vmm/intel/vmx.c
+++ sys/amd64/vmm/intel/vmx.c
@@ -191,8 +191,11 @@
static int guest_l1d_flush;
SYSCTL_INT(_hw_vmm_vmx, OID_AUTO, l1d_flush, CTLFLAG_RD,
&guest_l1d_flush, 0, NULL);
+static int guest_l1d_flush_sw;
+SYSCTL_INT(_hw_vmm_vmx, OID_AUTO, l1d_flush_sw, CTLFLAG_RD,
+ &guest_l1d_flush_sw, 0, NULL);
-uint64_t vmx_msr_flush_cmd;
+static struct msr_entry msr_load_list[1] __aligned(16);
/*
* The definitions of SDT probes for VMX.
@@ -579,6 +582,9 @@
vpid_unr = NULL;
}
+ if (nmi_flush_l1d_sw == 1)
+ nmi_flush_l1d_sw = 0;
+
smp_rendezvous(NULL, vmx_disable, NULL, NULL);
return (0);
@@ -807,9 +813,28 @@
guest_l1d_flush = (cpu_ia32_arch_caps & IA32_ARCH_CAP_RDCL_NO) == 0;
TUNABLE_INT_FETCH("hw.vmm.l1d_flush", &guest_l1d_flush);
- if (guest_l1d_flush &&
- (cpu_stdext_feature3 & CPUID_STDEXT3_L1D_FLUSH) != 0)
- vmx_msr_flush_cmd = IA32_FLUSH_CMD_L1D;
+
+ /*
+ * L1D cache flush is enabled. Use IA32_FLUSH_CMD MSR when
+ * available. Otherwise fall back to the software flush
+ * method which loads enough data from the kernel text to
+ * flush existing L1D content, both on VMX entry and on NMI
+ * return.
+ */
+ if (guest_l1d_flush) {
+ if ((cpu_stdext_feature3 & CPUID_STDEXT3_L1D_FLUSH) == 0) {
+ guest_l1d_flush_sw = 1;
+ TUNABLE_INT_FETCH("hw.vmm.l1d_flush_sw",
+ &guest_l1d_flush_sw);
+ }
+ if (guest_l1d_flush_sw) {
+ if (nmi_flush_l1d_sw <= 1)
+ nmi_flush_l1d_sw = 1;
+ } else {
+ msr_load_list[0].index = MSR_IA32_FLUSH_CMD;
+ msr_load_list[0].val = IA32_FLUSH_CMD_L1D;
+ }
+ }
/*
* Stash the cr0 and cr4 bits that must be fixed to 0 or 1
@@ -1000,6 +1025,15 @@
error += vmwrite(VMCS_MSR_BITMAP, vtophys(vmx->msr_bitmap));
error += vmwrite(VMCS_VPID, vpid[i]);
+ if (guest_l1d_flush && !guest_l1d_flush_sw) {
+ vmcs_write(VMCS_ENTRY_MSR_LOAD, pmap_kextract(
+ (vm_offset_t)&msr_load_list[0]));
+ vmcs_write(VMCS_ENTRY_MSR_LOAD_COUNT,
+ nitems(msr_load_list));
+ vmcs_write(VMCS_EXIT_MSR_STORE, 0);
+ vmcs_write(VMCS_EXIT_MSR_STORE_COUNT, 0);
+ }
+
/* exception bitmap */
if (vcpu_trace_exceptions(vm, i))
exc_bitmap = 0xffffffff;
Index: sys/amd64/vmm/intel/vmx_support.S
===================================================================
--- sys/amd64/vmm/intel/vmx_support.S
+++ sys/amd64/vmm/intel/vmx_support.S
@@ -176,44 +176,10 @@
jbe invept_error /* Check invept instruction error */
guest_restore:
-
- /*
- * Flush L1D cache if requested. Use IA32_FLUSH_CMD MSR if available,
- * otherwise load enough of the data from the zero_region to flush
- * existing L1D content.
- */
-#define L1D_FLUSH_SIZE (64 * 1024)
movl %edx, %r8d
- cmpb $0, guest_l1d_flush(%rip)
+ cmpb $0, guest_l1d_flush_sw(%rip)
je after_l1d
- movq vmx_msr_flush_cmd(%rip), %rax
- testq %rax, %rax
- jz 1f
- movq %rax, %rdx
- shrq $32, %rdx
- movl $MSR_IA32_FLUSH_CMD, %ecx
- wrmsr
- jmp after_l1d
-1: movq $KERNBASE, %r9
- movq $-L1D_FLUSH_SIZE, %rcx
- /*
- * pass 1: Preload TLB.
- * Kernel text is mapped using superpages. TLB preload is
- * done for the benefit of older CPUs which split 2M page
- * into 4k TLB entries.
- */
-2: movb L1D_FLUSH_SIZE(%r9, %rcx), %al
- addq $PAGE_SIZE, %rcx
- jne 2b
- xorl %eax, %eax
- cpuid
- movq $-L1D_FLUSH_SIZE, %rcx
- /* pass 2: Read each cache line */
-3: movb L1D_FLUSH_SIZE(%r9, %rcx), %al
- addq $64, %rcx
- jne 3b
- lfence
-#undef L1D_FLUSH_SIZE
+ call flush_l1d_sw
after_l1d:
cmpl $0, %r8d
je do_launch

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