[Qemu-devel] [PATCH v4 4/5] Don't use unreserved memory in BIOS.

[Gleb Natapov]

Use only first page and last page of low memory. OSes assumes that first
page is used by bios and last page is reserved in e820 map.

Signed-off-by: Gleb Natapov <address@hidden>
---

 bios/rombios.c        |   11 +++++++----
 bios/rombios.h        |    1 -
 bios/rombios32.c      |   11 ++++-------
 bios/rombios32start.S |    2 +-
 4 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/bios/rombios.c b/bios/rombios.c
index 4e555a9..5a56716 100644
--- a/bios/rombios.c
+++ b/bios/rombios.c
@@ -4548,7 +4548,7 @@ ASM_END
                 {
                     case 0:
                         set_e820_range(ES, regs.u.r16.di,
-                                       0x0000000L, 0x0009fc00L, 1);
+                                       0x0000000L, 0x0009f000L, 1);
                         regs.u.r32.ebx = 1;
                         regs.u.r32.eax = 0x534D4150;
                         regs.u.r32.ecx = 0x14;
@@ -4557,7 +4557,7 @@ ASM_END
                         break;
                     case 1:
                         set_e820_range(ES, regs.u.r16.di,
-                                       0x0009fc00L, 0x000a0000L, 2);
+                                       0x0009f000L, 0x000a0000L, 2);
                         regs.u.r32.ebx = 2;
                         regs.u.r32.eax = 0x534D4150;
                         regs.u.r32.ecx = 0x14;
@@ -10036,8 +10036,11 @@ rombios32_05:
   mov gs, ax
   cld
 
-  ;; init the stack pointer
-  mov esp, #0x00080000
+  ;; init the stack pointer to point below EBDA
+  mov ax, [0x040e]
+  shl eax, #4
+  mov esp, #-0x10
+  add esp, eax
 
   ;; pass pointer to s3_resume_flag and s3_resume_vector to rombios32
   push #0x04b0
diff --git a/bios/rombios.h b/bios/rombios.h
index f0ed88e..b3df88b 100644
--- a/bios/rombios.h
+++ b/bios/rombios.h
@@ -56,7 +56,6 @@
 #define ACPI_DATA_SIZE    0x00010000L
 #define PM_IO_BASE        0xb000
 #define SMB_IO_BASE       0xb100
-#define CPU_COUNT_ADDR    0xf000
 
   // Define the application NAME
 #if defined(BX_QEMU)
diff --git a/bios/rombios32.c b/bios/rombios32.c
index 7075aa9..0363e41 100644
--- a/bios/rombios32.c
+++ b/bios/rombios32.c
@@ -57,7 +57,7 @@ typedef unsigned long long uint64_t;
 
 #define APIC_ENABLED 0x0100
 
-#define AP_BOOT_ADDR 0x10000
+#define AP_BOOT_ADDR 0x9f000
 
 #define MPTABLE_MAX_SIZE  0x00002000
 #define SMI_CMD_IO_ADDR   0xb2
@@ -392,7 +392,7 @@ void delay_ms(int n)
     }
 }
 
-int smp_cpus;
+uint16_t smp_cpus;
 uint32_t cpuid_signature;
 uint32_t cpuid_features;
 uint32_t cpuid_ext_features;
@@ -495,7 +495,7 @@ void smp_probe(void)
 {
     uint32_t val, sipi_vector;
 
-    smp_cpus = 1;
+    writew(&smp_cpus, 1);
     if (cpuid_features & CPUID_APIC) {
 
         /* enable local APIC */
@@ -503,7 +503,6 @@ void smp_probe(void)
         val |= APIC_ENABLED;
         writel(APIC_BASE + APIC_SVR, val);
 
-        writew((void *)CPU_COUNT_ADDR, 1);
         /* copy AP boot code */
         memcpy((void *)AP_BOOT_ADDR, &smp_ap_boot_code_start,
                &smp_ap_boot_code_end - &smp_ap_boot_code_start);
@@ -514,10 +513,8 @@ void smp_probe(void)
         writel(APIC_BASE + APIC_ICR_LOW, 0x000C4600 | sipi_vector);
 
         delay_ms(10);
-
-        smp_cpus = readw((void *)CPU_COUNT_ADDR);
     }
-    BX_INFO("Found %d cpu(s)\n", smp_cpus);
+    BX_INFO("Found %d cpu(s)\n", readw(&smp_cpus));
 }
 
 /****************************************************/
diff --git a/bios/rombios32start.S b/bios/rombios32start.S
index 1900261..836652c 100644
--- a/bios/rombios32start.S
+++ b/bios/rombios32start.S
@@ -49,7 +49,7 @@ _start:
 smp_ap_boot_code_start:
   xor %ax, %ax
   mov %ax, %ds
-  lock incw CPU_COUNT_ADDR
+  lock incw smp_cpus
 1:
   hlt
   jmp 1b