i386: implement IGNNE

Change the handling of port F0h writes and FPU exceptions to implement IGNNE.

The implementation mixes a bit what the chipset and processor do in real
hardware, but the effect is the same as what happens with actual FERR#
and IGNNE# pins: writing to port F0h asserts IGNNE# in addition to lowering
FP_IRQ; while clearing the SE bit in the FPU status word deasserts IGNNE#.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 30 insertions, 8 deletions

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 01e052b3ba..5352c9ff55 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -203,6 +203,7 @@ typedef enum X86Seg {
 #define HF2_SMM_INSIDE_NMI_SHIFT 4 /* CPU serving SMI nested inside NMI */
 #define HF2_MPX_PR_SHIFT         5 /* BNDCFGx.BNDPRESERVE */
 #define HF2_NPT_SHIFT            6 /* Nested Paging enabled */
+#define HF2_IGNNE_SHIFT          7 /* Ignore CR0.NE=0 */
 
 #define HF2_GIF_MASK            (1 << HF2_GIF_SHIFT)
 #define HF2_HIF_MASK            (1 << HF2_HIF_SHIFT)
@@ -211,6 +212,7 @@ typedef enum X86Seg {
 #define HF2_SMM_INSIDE_NMI_MASK (1 << HF2_SMM_INSIDE_NMI_SHIFT)
 #define HF2_MPX_PR_MASK         (1 << HF2_MPX_PR_SHIFT)
 #define HF2_NPT_MASK            (1 << HF2_NPT_SHIFT)
+#define HF2_IGNNE_MASK          (1 << HF2_IGNNE_SHIFT)
 
 #define CR0_PE_SHIFT 0
 #define CR0_MP_SHIFT 1
@@ -1762,7 +1764,7 @@ int cpu_x86_support_mca_broadcast(CPUX86State *env);
 int cpu_get_pic_interrupt(CPUX86State *s);
 /* MSDOS compatibility mode FPU exception support */
 void x86_register_ferr_irq(qemu_irq irq);
-void cpu_clear_ferr(void);
+void cpu_set_ignne(void);
 /* mpx_helper.c */
 void cpu_sync_bndcs_hflags(CPUX86State *env);
 
diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
index 6825024f5c..99f28f267f 100644
--- a/target/i386/fpu_helper.c
+++ b/target/i386/fpu_helper.c
@@ -70,14 +70,24 @@ void x86_register_ferr_irq(qemu_irq irq)
     ferr_irq = irq;
 }
 
-void cpu_clear_ferr(void)
+static void cpu_clear_ignne(void)
 {
-    qemu_irq_lower(ferr_irq);
+    CPUX86State *env = &X86_CPU(first_cpu)->env;
+    env->hflags2 &= ~HF2_IGNNE_MASK;
 }
 
-static void cpu_set_ferr(void)
+void cpu_set_ignne(void)
 {
-    qemu_irq_raise(ferr_irq);
+    CPUX86State *env = &X86_CPU(first_cpu)->env;
+    env->hflags2 |= HF2_IGNNE_MASK;
+    /*
+     * We get here in response to a write to port F0h.  The chipset should
+     * deassert FP_IRQ and FERR# instead should stay signaled until FPSW_SE is
+     * cleared, because FERR# and FP_IRQ are two separate pins on real
+     * hardware.  However, we don't model FERR# as a qemu_irq, so we just
+     * do directly what the chipset would do, i.e. deassert FP_IRQ.
+     */
+    qemu_irq_lower(ferr_irq);
 }
 #endif
 
@@ -160,8 +170,8 @@ static void fpu_raise_exception(CPUX86State *env, uintptr_t retaddr)
         raise_exception_ra(env, EXCP10_COPR, retaddr);
     }
 #if !defined(CONFIG_USER_ONLY)
-    else {
-        cpu_set_ferr();
+    else if (ferr_irq && !(env->hflags2 & HF2_IGNNE_MASK)) {
+        qemu_irq_raise(ferr_irq);
     }
 #endif
 }
@@ -1056,7 +1066,17 @@ void helper_fstenv(CPUX86State *env, target_ulong ptr, int data32)
 static void cpu_set_fpus(CPUX86State *env, uint16_t fpus)
 {
     env->fpstt = (fpus >> 11) & 7;
-    env->fpus = fpus & ~0x3800;
+    env->fpus = fpus & ~0x3800 & ~FPUS_B;
+    env->fpus |= env->fpus & FPUS_SE ? FPUS_B : 0;
+#if !defined(CONFIG_USER_ONLY)
+    if (!(env->fpus & FPUS_SE)) {
+        /*
+         * Here the processor deasserts FERR#; in response, the chipset deasserts
+         * IGNNE#.
+         */
+        cpu_clear_ignne();
+    }
+#endif
 }
 
 static void do_fldenv(CPUX86State *env, target_ulong ptr, int data32,