xv6/mp.c

// Multiprocessor support
// Search memory for MP description structures.
// http://developer.intel.com/design/pentium/datashts/24201606.pdf

#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mp.h"
#include "x86.h"
#include "mmu.h"
#include "proc.h"

struct cpu cpus[NCPU];
int ncpu;
uchar ioapicid;

static uchar sum(uchar *addr, int len)  {
    int i, sum;

    sum = 0;
    for (i = 0; i < len; i++) {
        sum += addr[i];
    }
    return sum;
}

// Look for an MP structure in the len bytes at addr.
static struct mp*mpsearch1(uint a, int len) {
    uchar *e, *p, *addr;

    addr = P2V(a);
    e = addr + len;
    for (p = addr; p < e; p += sizeof(struct mp)) {
        if (memcmp(p, "_MP_", 4) == 0 && sum(p, sizeof(struct mp)) == 0) {
            return (struct mp*)p;
        }
    }
    return 0;
}

// Search for the MP Floating Pointer Structure, which according to the
// spec is in one of the following three locations:
// 1) in the first KB of the EBDA;
// 2) in the last KB of system base memory;
// 3) in the BIOS ROM between 0xE0000 and 0xFFFFF.
static struct mp*mpsearch(void) {
    uchar *bda;
    uint p;
    struct mp *mp;

    bda = (uchar *) P2V(0x400);
    if ((p = ((bda[0x0F] << 8) | bda[0x0E]) << 4)) {
        if ((mp = mpsearch1(p, 1024))) {
            return mp;
        }
    }
    else {
        p = ((bda[0x14] << 8) | bda[0x13]) * 1024;
        if ((mp = mpsearch1(p - 1024, 1024))) {
            return mp;
        }
    }
    return mpsearch1(0xF0000, 0x10000);
}

// Search for an MP configuration table.  For now,
// don't accept the default configurations (physaddr == 0).
// Check for correct signature, calculate the checksum and,
// if correct, check the version.
// To do: check extended table checksum.
static struct mpconf*mpconfig(struct mp **pmp) {
    struct mpconf *conf;
    struct mp *mp;

    if ((mp = mpsearch()) == 0 || mp->physaddr == 0) {
        return 0;
    }
    conf = (struct mpconf*) P2V((uint) mp->physaddr);
    if (memcmp(conf, "PCMP", 4) != 0) {
        return 0;
    }
    if (conf->version != 1 && conf->version != 4) {
        return 0;
    }
    if (sum((uchar*)conf, conf->length) != 0) {
        return 0;
    }
    *pmp = mp;
    return conf;
}

void mpinit(void) {
    uchar *p, *e;
    int ismp;
    struct mp *mp;
    struct mpconf *conf;
    struct mpproc *proc;
    struct mpioapic *ioapic;

    if ((conf = mpconfig(&mp)) == 0) {
        panic("Expect to run on an SMP");
    }
    ismp = 1;
    lapic = (uint*)conf->lapicaddr;
    for (p = (uchar*)(conf + 1), e = (uchar*)conf + conf->length; p < e;) {
        switch (*p) {
            case MPPROC:
                proc = (struct mpproc*)p;
                if (ncpu < NCPU) {
                    cpus[ncpu].apicid = proc->apicid;  // apicid may differ from ncpu
                    ncpu++;
                }
                p += sizeof(struct mpproc);
                continue;
            case MPIOAPIC:
                ioapic = (struct mpioapic*)p;
                ioapicid = ioapic->apicno;
                p += sizeof(struct mpioapic);
                continue;
            case MPBUS:
            case MPIOINTR:
            case MPLINTR:
                p += 8;
                continue;
            default:
                ismp = 0;
                break;
        }
    }
    if (!ismp) {
        panic("Didn't find a suitable machine");
    }

    if (mp->imcrp) {
        // Bochs doesn't support IMCR, so this doesn't run on Bochs.
        // But it would on real hardware.
        outb(0x22, 0x70);   // Select IMCR
        outb(0x23, inb(0x23) | 1);  // Mask external interrupts.
    }
}