On Sun, Feb 5, 2023 at 5:20 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
@@ -53,7 +53,8 @@ static inline u8 mtrr_type_lookup(u64 addr,
/*
* Return no-MTRRs:
*/
- return MTRR_TYPE_INVALID;
+ *uniform = 1;
+ return MTRR_TYPE_UNCACHABLE;
So this is the one I'd almost leave alone.
Because this is not a "there are no MTRR's" situation, this is a "I
haven't enabled CONFIG_MTRR, so I don't _know_ if there are any MTRR's
or not.
And returning MTRR_TYPE_UNCACHABLE will then disable things like
largepages etc, so this change would effectively mean that if
CONFIG_MTRR is off, it would turn off hugepage support too.
But maybe that was the only thing that cared, and we have:
@@ -721,8 +721,9 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
u8 mtrr, uniform;
mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE, &uniform);
- if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
- (mtrr != MTRR_TYPE_WRBACK))
+ if (mtrr != MTRR_TYPE_UNCACHABLE &&
+ mtrr != MTRR_TYPE_WRBACK &&
+ !uniform)
return 0;
Here you make up for it, but I don't actually understand why these
checks exist at all.
I *think* that what the check should do is just check for uniformity.
Why would the largepage code otherwise care?
Other MTRR types are explicitly fine, and I think things like the X
server might even want to do write-combining with large pages etc.
So I think the hugepage code should only do
if (!uniform)
return 0;
or there should be some explanation for why those types are special?
@@ -748,8 +749,9 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)u8 mtrr, uniform;
mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE, &uniform);
- if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
- (mtrr != MTRR_TYPE_WRBACK)) {
+ if (mtrr != MTRR_TYPE_UNCACHABLE &&
+ mtrr != MTRR_TYPE_WRBACK &&
+ !uniform) {
Same here.
Again, I *think* that the reason it used to do that "check two types"
thing is simply because "uniform" wasn't set correctly.
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