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pc, pc64: exclude memory regions with unusual MTRR cache attributes

Use the MTRR registers to exclude memory ranges that
do not have the expected cache attributes:

RAM -> writeback
UMB -> uncached
UPA -> uncached

--- a/sys/src/9/pc/fns.h

+++ b/sys/src/9/pc/fns.h

@@ -101,6 +101,7 @@

 void	mmuinit(void);

 ulong*	mmuwalk(ulong*, ulong, int, int);

 char*	mtrr(uvlong, uvlong, char *);

+char*	mtrrattr(uvlong, uvlong *);

 void	mtrrclock(void);

 int	mtrrprint(char *, long);

 void	mtrrsync(void);

--- a/sys/src/9/pc/memory.c

+++ b/sys/src/9/pc/memory.c

@@ -320,6 +320,27 @@

 	}

 }

+static void

+mtrrexclude(int type, char *expect)

+{

+	uvlong base, top, next, pa;

+	char *attr;

+

+	for(base = memmapnext(-1, type); base != -1; base = memmapnext(base, type)){

+		top = base + memmapsize(base, 0);

+		for(pa = base; pa < top; pa = next){

+			next = top;

+			attr = mtrrattr(pa, &next);

+			if(attr != nil && strcmp(attr, expect) != 0){

+				if(next > top)

+					next = top;

+				memmapadd(pa, next - pa, MemReserved);

+			}

+			base = pa;

+		}

+	}

+}

+

 static int

 e820scan(void)

 {

@@ -362,6 +383,9 @@

 		}

 	}

+	/* RAM needs to be writeback */

+	mtrrexclude(MemRAM, "wb");

+

 	for(base = memmapnext(-1, MemRAM); base != -1; base = memmapnext(base, MemRAM)){

 		size = memmapsize(base, BY2PG) & ~(BY2PG-1);

 		if(size != 0)

@@ -376,6 +400,7 @@

 {

 	ulong save, pat, seed, *v, *k0;

 	int i, n, w;

+	char *attr;

 	pa += chunk-1;

 	pa &= ~(chunk-1);

@@ -389,6 +414,10 @@

 	pat = 0x12345678UL;

 	for(; pa < top; pa += chunk){

+		attr = mtrrattr(pa, nil);

+		if(attr != nil && strcmp(attr, "wb") != 0)

+			goto Skip;

+

 		/* write pattern */

 		seed = pat;

 		if((v = vmap(pa, chunk)) == nil)

@@ -420,6 +449,7 @@

 	Bad:

 		vunmap(v, chunk);

+	Skip:

 		if(pa+chunk <= 16*MB)

 			memmapadd(pa, chunk, MemUMB);

@@ -488,6 +518,12 @@

 	 */

 	if(e820scan() < 0)

 		ramscan(MemMin, -((uintptr)MemMin), 4*MB);

+

+	/*

+	 * Exclude UMB's and UPA's with unusual cache attributes.

+	 */

+	mtrrexclude(MemUMB, "uc");

+	mtrrexclude(MemUPA, "uc");

 }

 /*

--- a/sys/src/9/pc/mtrr.c

+++ b/sys/src/9/pc/mtrr.c

@@ -691,6 +691,16 @@

 	return nil;

 }

+char*

+mtrrattr(uvlong pa, uvlong *pnext)

+{

+	if(cpu0state.mask == 0)

+		return nil;

+	if(pnext != nil)

+		*pnext = getnext(&cpu0state, pa, nil);

+	return type2str(gettype(&cpu0state, pa, nil));

+}

+

 int

 mtrrprint(char *buf, long bufsize)

 {

--- a/sys/src/9/pc64/fns.h

+++ b/sys/src/9/pc64/fns.h

@@ -99,6 +99,7 @@

 void	mmuinit(void);

 uintptr	*mmuwalk(uintptr*, uintptr, int, int);

 char*	mtrr(uvlong, uvlong, char *);

+char*	mtrrattr(uvlong, uvlong *);

 void	mtrrclock(void);

 int	mtrrprint(char *, long);

 void	mtrrsync(void);