The aliasing doesn't matter for Linux because we map the high and low half the same. Henrique de Moraes Holschuh <hmh@xxxxxxxxxx> wrote: >On Sun, 23 Jun 2013, H. Peter Anvin wrote: >> On 06/23/2013 02:56 PM, Henrique de Moraes Holschuh wrote: >> > >> > And as far as I could find from Intel's not-that-complete public >> > "specification updates", we are applying the errata workaround to a >few more >> > processors than strictly required, but since I have no idea how to >write a >> > test case, I can't whitelist the 3rd-gen Pentium M on my T43, nor >can I get >> > ThinkPad owners to test it for us on 1st and 2nd-gen Pentium M and >report >> > back. >> >> Which specific erratum are you referring to, here? The "WC becomes >UC" >> erratum? I don't think there is a sane testcase for it since it >needs a >> very complicated setup to trigger. > >There are at least two different nasty PAT issues that are not always >critical, and one that outright hangs the processor (if the unsupported >aliasing of WB with UC/WC happens). > >Interestingly enough, most of the P4-Xeons and P4 do not appear to have >the >"WC becomes UC" errata. > >However, LOTS of P4, M-P4, Xeon PIII, Xeon, and Pentium M have a bug >where >the four highest entries in the PAT table are inactive (aliased to the >four >lowest entries) in mode B (PSE) and mode C (PAE) for 4k pages. They >work >fine for large pages. > >Also, lots of them can hang if you ever alias WB with UC or WC (which >is >apparently an unsupported configuration anyway, or so it says in the >errata). > >There are other weird aliasing nasties, such as one where you get >memory >corruption if you alias WB data with code (being accessed as UC or WC) >in >the same cacheline, and some stuff such as weirdness should the page >table >be on WC memory... > >I can track down most of the CPUIDs involved if you want, but someone >from >Intel would be better (I assume they actually have access to the errata >documentation in some less idiotic way than reading a ton of badly >indexed >PDFs that take forever to find in their site). -- Sent from my mobile phone. Please excuse brevity and lack of formatting. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
