Messages in this thread | | | Date | Sun, 27 Oct 2013 14:34:01 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] X86: MM: Add PAT Type write-through in combination with mtrr |
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On Sun, Oct 27, 2013 at 01:55:25PM +0100, Andreas Werner wrote: > This patch adds the Write-through memory type in combination with mtrr. > If you call ioremap_cache to request cachable memory (write-back) the > function tries to set the PAT to write-back only if the mtrr setting of > the requested region is also marked as Write-Back. > If the mttr regions are marked e.g. as Write-through or with other > types, the function will always return UC- memory. > > If you check the Intel document " IA-32 SDM vol 3a table Effective > Memory Type", there > are many other combinations possible. > > This patch will only add the following combination: > PAT=Write-Back + MTRR=Write-Through = Effective Memory of > Write-Through
And yet the code below returns WB for WT MTRR type which can't be right since having a write-through mapping cannot be compatible with write-back as the last caches writes into the cache instead of writing them through to memory.
Why do you even care about WT? Are you trying to fix a bug or what?
> Tested on - Intel (R) Atom E680 (Tunnel Creek) > - Intel (R) Core(TM)2 Duo > > Signed-off-by: Andreas Werner <wernerandy@gmx.de> > --- > arch/x86/mm/pat.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c > index 6574388..9cfe107 100644 > --- a/arch/x86/mm/pat.c > +++ b/arch/x86/mm/pat.c > @@ -149,10 +149,15 @@ static unsigned long pat_x_mtrr_type(u64 start, u64 end, unsigned long req_type) > u8 mtrr_type; > > mtrr_type = mtrr_type_lookup(start, end); > - if (mtrr_type != MTRR_TYPE_WRBACK) > - return _PAGE_CACHE_UC_MINUS; > > - return _PAGE_CACHE_WB; > + switch (mtrr_type) { > + case MTRR_TYPE_WRBACK: > + case MTRR_TYPE_WRTHROUGH: > + return _PAGE_CACHE_WB; > + > + default: > + return _PAGE_CACHE_UC_MINUS; > + } > } > > return req_type;
-- Regards/Gruss, Boris.
Sent from a fat crate under my desk. Formatting is fine. --
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