[SeaBIOS] [PATCH v4 3/5] error out if present cpus count changed during SMP bringup

[Igor Mammedov]

if during SMP bringup a cpu is hotplugged, Seabios might
silently hung in

while (cmos_smp_count != CountCPUs)

loop as cmos_smp_count might be less then CountCPUs if
SIPI were delivered to the hotplugged CPU.

Warn user about it and ask for reboot.

While at it rename CountCPUs to BroughtUpCPUs to make clear
what it is counting.

Signed-off-by: Igor Mammedov 
---
 src/fw/smp.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/fw/smp.c b/src/fw/smp.c
index 31bcc6a..9040b01 100644
--- a/src/fw/smp.c
+++ b/src/fw/smp.c
@@ -46,7 +46,7 @@ smp_write_msrs(void)
 }

u32 MaxCountCPUs;
-static u32 CountCPUs;
+static u32 BroughtUpCPUs;
 // 256 bits for the found APIC IDs
 static u32 FoundAPICIDs[256/32];

@@ -78,7 +78,7 @@ handle_smp(void)

smp_write_msrs();

-    CountCPUs++;
+    BroughtUpCPUs++;
 }

// Atomic lock for shared stack across processors.
@@ -95,13 +95,13 @@ smp_scan(void)
     if (eax < 1 || !(cpuid_features & CPUID_APIC)) {
         // No apic - only the main cpu is present.
         dprintf(1, "No apic - only the main cpu is present.\n");
-        CountCPUs= 1;
+        BroughtUpCPUs= 1;
         return;
     }

// mark the BSP initial APIC ID as found, too:
     apic_id_init();
-    CountCPUs = 1;
+    BroughtUpCPUs = 1;

// Setup jump trampoline to counter code.
     u64 old = *(u64*)BUILD_AP_BOOT_ADDR;
@@ -131,8 +131,8 @@ smp_scan(void)
     writel(APIC_ICR_LOW, 0x000C4600 | sipi_vector);

// Wait for other CPUs to process the SIPI.
-    u8 cmos_smp_count = rtc_read(CMOS_BIOS_SMP_COUNT) + 1;
-    while (cmos_smp_count != CountCPUs)
+    u8 smp_count, smp_count_initial = rtc_read(CMOS_BIOS_SMP_COUNT) + 1;
+    while ((smp_count = rtc_read(CMOS_BIOS_SMP_COUNT) + 1) != BroughtUpCPUs) {
         asm volatile(
             // Release lock and allow other processors to use the stack.
             "  movl %%esp, %1\n"
@@ -143,12 +143,15 @@ smp_scan(void)
             "  jc 1b\n"
             : "+m" (SMPLock), "+m" (SMPStack)
             : : "cc", "memory");
+        if (smp_count != smp_count_initial)
+            dprintf(1, "Error: count of present cpus changed, reboot manually");
+    }
     yield();

// Restore memory.
     *(u64*)BUILD_AP_BOOT_ADDR = old;

-    dprintf(1, "Found %d cpu(s) max supported %d cpu(s)\n", CountCPUs,
+    dprintf(1, "Found %d cpu(s) max supported %d cpu(s)\n", BroughtUpCPUs,
             MaxCountCPUs);
 }