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 <toshi.kani@xxxxxx>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> 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.
> 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?
Thanks,
tglx
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