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pc, pc64: preserve last KB of conventional memory (might contain bios tables)

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we add new function convmemsize() that returns the size of
*usable* conventional memory that does some sanity checking
and reserves the last KB below the top of memory pointer.

this avoids lowraminit() overriding potential bios tables
and sigsearch() going off the rails looking for tables
at above 640K.
This commit is contained in:
cinap_lenrek 2014-11-20 19:05:43 +01:00
parent 5a6131ea09
commit 529082d34d
2 changed files with 44 additions and 20 deletions
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34
sys/src/9/pc/memory.c
View file

@ -340,6 +340,24 @@ sigscan(uchar* addr, int len, char* signature)
return nil;
}
static uintptr
convmemsize(void)
{
uintptr top;
uchar *bda;
bda = KADDR(0x400);
top = ((bda[0x14]<<8) | bda[0x13])*KB;
if(top < 64*KB || top > 640*KB)
top = 640*KB; /* sanity */
/* reserved for bios tables (EBDA) */
top -= 1*KB;
return top;
}
void*
sigsearch(char* signature)
{
@ -362,11 +380,9 @@ sigsearch(char* signature)
return r;
}
}
if((r = sigscan(KADDR(convmemsize()), 1024, signature)) != nil)
return r;
if((p = ((bda[0x14]<<8)|bda[0x13])*1024) != 0){
if((r = sigscan(KADDR(p-1024), 1024, signature)) != nil)
return r;
}
/* hack for virtualbox: look in KiB below 0xa0000 */
if((r = sigscan(KADDR(0xa0000-1024), 1024, signature)) != nil)
return r;
@ -377,8 +393,7 @@ sigsearch(char* signature)
static void
lowraminit(void)
{
ulong pa, x;
uchar *bda;
uintptr pa, x;
/*
* Initialise the memory bank information for conventional memory
@ -387,16 +402,13 @@ lowraminit(void)
* the BIOS data area.
*/
x = PADDR(CPU0END);
bda = (uchar*)KADDR(0x400);
pa = ((bda[0x14]<<8)|bda[0x13])*KB;
if(pa > 640*KB)
pa = 640*KB;
pa = convmemsize();
if(x < pa){
mapfree(&rmapram, x, pa-x);
memset(KADDR(x), 0, pa-x); /* keep us honest */
}
x = PADDR(PGROUND((ulong)end));
x = PADDR(PGROUND((uintptr)end));
pa = MemMin;
if(x > pa)
panic("kernel too big");

30
sys/src/9/pc64/memory.c
View file

@ -337,6 +337,24 @@ sigscan(uchar* addr, int len, char* signature)
return nil;
}
static uintptr
convmemsize(void)
{
uintptr top;
uchar *bda;
bda = KADDR(0x400);
top = ((bda[0x14]<<8) | bda[0x13])*KB;
if(top < 64*KB || top > 640*KB)
top = 640*KB; /* sanity */
/* reserved for bios tables (EBDA) */
top -= 1*KB;
return top;
}
void*
sigsearch(char* signature)
{
@ -359,11 +377,9 @@ sigsearch(char* signature)
return r;
}
}
if((r = sigscan(KADDR(convmemsize()), 1024, signature)) != nil)
return r;
if((p = ((bda[0x14]<<8)|bda[0x13])*1024) != 0){
if((r = sigscan(KADDR(p-1024), 1024, signature)) != nil)
return r;
}
/* hack for virtualbox: look in KiB below 0xa0000 */
if((r = sigscan(KADDR(0xa0000-1024), 1024, signature)) != nil)
return r;
@ -375,7 +391,6 @@ static void
lowraminit(void)
{
uintptr pa, x;
uchar *bda;
/*
* Initialise the memory bank information for conventional memory
@ -384,10 +399,7 @@ lowraminit(void)
* the BIOS data area.
*/
x = PADDR(CPU0END);
bda = (uchar*)KADDR(0x400);
pa = ((bda[0x14]<<8)|bda[0x13])*KB;
if(pa > 640*KB)
pa = 640*KB;
pa = convmemsize();
if(x < pa){
mapfree(&rmapram, x, pa-x);
memset(KADDR(x), 0, pa-x); /* keep us honest */