On Mon, 2014-11-03 at 19:27 +0100, Thomas Gleixner wrote:
> On Mon, 27 Oct 2014, Toshi Kani wrote:
> > This patch changes reserve_memtype() to handle the WT cache mode.
> > When PAT is not enabled, it continues to set UC- to *new_type for
> > any non-WB request.
> >
> > When a target range is RAM, reserve_ram_pages_type() fails for WT
> > for now. This function may not reserve a RAM range for WT since
> > reserve_ram_pages_type() uses the page flags limited to three memory
> > types, WB, WC and UC.
> >
> > Signed-off-by: Toshi Kani <[email protected]>
> > Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
> > ---
> > arch/x86/include/asm/cacheflush.h | 4 ++++
> > arch/x86/mm/pat.c | 16 +++++++++++++---
> > 2 files changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/cacheflush.h
> > b/arch/x86/include/asm/cacheflush.h
> > index 157644b..c912680 100644
> > --- a/arch/x86/include/asm/cacheflush.h
> > +++ b/arch/x86/include/asm/cacheflush.h
> > @@ -53,6 +53,10 @@ static inline void set_page_memtype(struct page *pg,
> > case _PAGE_CACHE_MODE_WB:
> > memtype_flags = _PGMT_WB;
> > break;
> > + case _PAGE_CACHE_MODE_WT:
> > + case _PAGE_CACHE_MODE_WP:
> > + pr_err("set_page_memtype: unsupported cachemode %d\n", memtype);
> > + BUG();
>
> You already catch the cases with the hunk below at the entry of
> reserve_ram_pages_type(). So what's the point of the BUG()?
>
> If you are worried about other usage sites: This function should not
> at all be in arch/x86/include/asm/cacheflush.h. It's solely used by
> PAT, so we really should move it there before changing it.
Yes, I was worried about other usage. I agree that this function should
belong to PAT. I will move it to pat.c before changing it, and will
remove BUG() from this patch.
> > default:
> > memtype_flags = _PGMT_DEFAULT;
> > break;
> > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> > index db687c3..a214f5a 100644
> > --- a/arch/x86/mm/pat.c
> > +++ b/arch/x86/mm/pat.c
> > @@ -289,6 +289,8 @@ static int pat_pagerange_is_ram(resource_size_t start,
> > resource_size_t end)
> >
> > /*
> > * For RAM pages, we use page flags to mark the pages with appropriate
> > type.
> > + * The page flags are currently limited to three types, WB, WC and UC.
> > Hence,
> > + * any request to WT or WP will fail with -EINVAL.
> > * Here we do two pass:
> > * - Find the memtype of all the pages in the range, look for any conflicts
> > * - In case of no conflicts, set the new memtype for pages in the range
> > @@ -300,6 +302,13 @@ static int reserve_ram_pages_type(u64 start, u64 end,
> > struct page *page;
> > u64 pfn;
> >
> > + if ((req_type == _PAGE_CACHE_MODE_WT) ||
> > + (req_type == _PAGE_CACHE_MODE_WP)) {
> > + if (new_type)
> > + *new_type = _PAGE_CACHE_MODE_UC_MINUS;
> > + return -EINVAL;
> > + }
> > +
> > if (req_type == _PAGE_CACHE_MODE_UC) {
> > /* We do not support strong UC */
> > WARN_ON_ONCE(1);
> > @@ -349,6 +358,7 @@ static int free_ram_pages_type(u64 start, u64 end)
> > * - _PAGE_CACHE_MODE_WC
> > * - _PAGE_CACHE_MODE_UC_MINUS
> > * - _PAGE_CACHE_MODE_UC
> > + * - _PAGE_CACHE_MODE_WT
> > *
> > * If new_type is NULL, function will return an error if it cannot reserve
> > the
> > * region with req_type. If new_type is non-NULL, function will return
> > @@ -368,10 +378,10 @@ int reserve_memtype(u64 start, u64 end, enum
> > page_cache_mode req_type,
> > if (!pat_enabled) {
> > /* This is identical to page table setting without PAT */
> > if (new_type) {
> > - if (req_type == _PAGE_CACHE_MODE_WC)
> > - *new_type = _PAGE_CACHE_MODE_UC_MINUS;
> > + if (req_type == _PAGE_CACHE_MODE_WB)
> > + *new_type = _PAGE_CACHE_MODE_WB;
> > else
> > - *new_type = req_type;
> > + *new_type = _PAGE_CACHE_MODE_UC_MINUS;
>
> So until now we supported WB, UC- and UC and mapped WC to UC-. Now we
> map everything except WB to UC-
> Why feels that wrong without a comment explaining it?
The case of !pat_enable only supports WB and UC-. Previously, WC was
the only type that needed to be mapped to UC-. The code now handles it
properly for any other types. Yes, I will add a comment for this.
Thanks,
-Toshi
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