[SeaBIOS] [PATCH 2/2] Always enable caching on transition32; backup/restore cr0 on call32

[Kevin O'Connor]

Always enable caching at start of 32bit code and always make sure the
paging flag is off.  Because this alters the cr0 register, perform a
backup and restore of it when using call32().

Also, rename get/setcr0() to cr0_read/write() to more closely match
other register access functions.

Signed-off-by: Kevin O'Connor 
---
 src/fw/smp.c    |  3 ---
 src/post.c      |  3 ---
 src/romlayout.S |  1 +
 src/stacks.c    | 45 ++++++++++++++++++++++++++++-----------------
 src/x86.h       |  9 ++++++---
 5 files changed, 35 insertions(+), 26 deletions(-)

diff --git a/src/fw/smp.c b/src/fw/smp.c
index a466ea6..579acdb 100644
--- a/src/fw/smp.c
+++ b/src/fw/smp.c
@@ -52,9 +52,6 @@ handle_smp(void)
     if (!CONFIG_QEMU)
         return;

-    // Enable CPU caching
-    setcr0(getcr0() & ~(CR0_CD|CR0_NW));
-
     // Detect apic_id
     u32 eax, ebx, ecx, cpuid_features;
     cpuid(1, &eax, &ebx, &ecx, &cpuid_features);
diff --git a/src/post.c b/src/post.c
index 6803585..e19b06c 100644
--- a/src/post.c
+++ b/src/post.c
@@ -158,9 +158,6 @@ device_hardware_setup(void)
 static void
 platform_hardware_setup(void)
 {
-    // Enable CPU caching
-    setcr0(getcr0() & ~(CR0_CD|CR0_NW));
-
     // Make sure legacy DMA isn't running.
     dma_setup();

diff --git a/src/romlayout.S b/src/romlayout.S
index fefc212..823188b 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -47,6 +47,7 @@ transition32_nmi_off:

// Enable protected mode
         movl %cr0, %ecx
+        andl $~(CR0_PG|CR0_CD|CR0_NW), %ecx
         orl $CR0_PE, %ecx
         movl %ecx, %cr0

diff --git a/src/stacks.c b/src/stacks.c
index a156138..fa9c7db 100644
--- a/src/stacks.c
+++ b/src/stacks.c
@@ -1,6 +1,6 @@
 // Code for manipulating stack locations.
 //
-// Copyright (C) 2009-2014  Kevin O'Connor 
+// Copyright (C) 2009-2015  Kevin O'Connor 
 //
 // This file may be distributed under the terms of the GNU LGPLv3 license.

@@ -28,6 +28,7 @@ struct {
     u8 cmosindex;
     u8 a20;
     u16 ss, fs, gs;
+    u32 cr0;
     struct descloc_s gdt;
 } Call16Data VARLOW;

@@ -37,19 +38,17 @@ struct {
 int HaveSmmCall32 VARFSEG;

// Backup state in preparation for call32
-static void
+static int
 call32_prep(u8 method)
 {
-    // Backup cmos index register and disable nmi
-    u8 cmosindex = inb(PORT_CMOS_INDEX);
-    outb(cmosindex | NMI_DISABLE_BIT, PORT_CMOS_INDEX);
-    inb(PORT_CMOS_DATA);
-    SET_LOW(Call16Data.cmosindex, cmosindex);
-
-    // Backup ss
-    SET_LOW(Call16Data.ss, GET_SEG(SS));
-
     if (!CONFIG_CALL32_SMM || method != C16_SMM) {
+        // Backup cr0
+        u32 cr0 = cr0_read();
+        if (cr0 & CR0_PE)
+            // Called in 16bit protected mode?!
+            return -1;
+        SET_LOW(Call16Data.cr0, cr0);
+
         // Backup fs/gs and gdt
         SET_LOW(Call16Data.fs, GET_SEG(FS));
         SET_LOW(Call16Data.gs, GET_SEG(GS));
@@ -62,7 +61,17 @@ call32_prep(u8 method)
         SET_LOW(Call16Data.a20, set_a20(1));
     }

+    // Backup ss
+    SET_LOW(Call16Data.ss, GET_SEG(SS));
+
+    // Backup cmos index register and disable nmi
+    u8 cmosindex = inb(PORT_CMOS_INDEX);
+    outb(cmosindex | NMI_DISABLE_BIT, PORT_CMOS_INDEX);
+    inb(PORT_CMOS_DATA);
+    SET_LOW(Call16Data.cmosindex, cmosindex);
+
     SET_LOW(Call16Data.method, method);
+    return 0;
 }

// Restore state backed up during call32
@@ -84,6 +93,11 @@ call32_post(void)
         lgdt(&gdt);
         SET_SEG(FS, GET_LOW(Call16Data.fs));
         SET_SEG(GS, GET_LOW(Call16Data.gs));
+
+        // Restore cr0
+        u32 cr0_caching = GET_LOW(Call16Data.cr0) & (CR0_CD|CR0_NW);
+        if (cr0_caching)
+            cr0_mask(CR0_CD|CR0_NW, cr0_caching);
     }

// Restore cmos index register
@@ -220,14 +234,11 @@ call32(void *func, u32 eax, u32 errret)
     ASSERT16();
     if (CONFIG_CALL32_SMM && GET_GLOBAL(HaveSmmCall32))
         return call32_smm(func, eax);
-    u32 cr0 = getcr0();
-    if (cr0 & CR0_PE)
-        // Called in 16bit protected mode?!
-        return errret;
-
     // Jump direclty to 32bit mode - this clobbers the 16bit segment
     // selector registers.
-    call32_prep(C16_BIG);
+    int ret = call32_prep(C16_BIG);
+    if (ret)
+        return errret;
     u32 bkup_ss, bkup_esp;
     asm volatile(
         // Backup ss/esp / set esp to flat stack location
diff --git a/src/x86.h b/src/x86.h
index 234a6e2..19d404f 100644
--- a/src/x86.h
+++ b/src/x86.h
@@ -75,15 +75,18 @@ static inline void __cpuid(u32 index, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
         : "0" (index));
 }

-static inline u32 getcr0(void) {
+static inline u32 cr0_read(void) {
     u32 cr0;
     asm("movl %%cr0, %0" : "=r"(cr0));
     return cr0;
 }
-static inline void setcr0(u32 cr0) {
+static inline void cr0_write(u32 cr0) {
     asm("movl %0, %%cr0" : : "r"(cr0));
 }
-static inline u16 getcr0_vm86(void) {
+static inline void cr0_mask(u32 off, u32 on) {
+    cr0_write((cr0_read() & ~off) | on);
+}
+static inline u16 cr0_vm86_read(void) {
     u16 cr0;
     asm("smsww %0" : "=r"(cr0));
     return cr0;