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guesscpuhz: add sanity checks for virtualbox (import from sources)

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This commit is contained in:
cinap_lenrek 2012-08-24 15:46:21 +02:00
parent d436b2117e
commit da01fdae11
1 changed files with 4 additions and 1 deletions
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5
sys/src/9/pc/i8253.c
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@ -165,7 +165,7 @@ guesscpuhz(int aalcycles)
cpufreq = (vlong)loops*((aalcycles*2*Freq)/x);
m->loopconst = (cpufreq/1000)/aalcycles; /* AAM+LOOP's for 1 ms */
if(m->havetsc){
if(m->havetsc && a != b){ /* a == b means virtualbox has confused us */
/* counter goes up by 2*Freq */
b = (b-a)<<1;
b *= Freq;
@ -185,6 +185,9 @@ guesscpuhz(int aalcycles)
m->cpuhz = cpufreq;
}
/* don't divide by zero in trap.c */
if(m->cpumhz == 0)
panic("guesscpuhz: zero m->cpumhz");
i8253.hz = Freq<<Tickshift;
}