On Fri, Jan 03, 2014 at 09:49:12AM -0700, Ian Lepore wrote: > On Wed, 2014-01-01 at 22:32 +0200, Konstantin Belousov wrote: > > On Wed, Jan 01, 2014 at 08:26:08PM +0000, Zbigniew Bodek wrote: > > > Author: zbb > > > Date: Wed Jan 1 20:26:08 2014 > > > New Revision: 260165 > > > URL: http://svnweb.freebsd.org/changeset/base/260165 > > > > > > Log: > > > Use only mapped BIOs on ARM > > > > > > Using unmapped BIOs causes failure inside bus_dmamap_sync, since > > > this function requires valid MVA address, which is not present > > > if mapping is not set up. > > > > > > Submitted by: Wojciech Macek <w...@semihalf.com> > > > Obtained from: Semihalf > > > > > > Modified: > > > head/sys/dev/ahci/ahci.c > > > > > > Modified: head/sys/dev/ahci/ahci.c > > > ============================================================================== > > > --- head/sys/dev/ahci/ahci.c Wed Jan 1 20:22:29 2014 > > > (r260164) > > > +++ head/sys/dev/ahci/ahci.c Wed Jan 1 20:26:08 2014 > > > (r260165) > > > @@ -3066,7 +3066,15 @@ ahciaction(struct cam_sim *sim, union cc > > > if (ch->caps & AHCI_CAP_SPM) > > > cpi->hba_inquiry |= PI_SATAPM; > > > cpi->target_sprt = 0; > > > +#ifdef __arm__ > > > + /* > > > + * Do not use unmapped buffers on ARM. Doing so will cause > > > + * failure inside bus_dmamap_sync due to lack of VA. > > > + */ > > > + cpi->hba_misc = PIM_SEQSCAN; > > > +#else > > > cpi->hba_misc = PIM_SEQSCAN | PIM_UNMAPPED; > > > +#endif > > > cpi->hba_eng_cnt = 0; > > > if (ch->caps & AHCI_CAP_SPM) > > > cpi->max_target = 15; > > > > I think this is wrong. If bus_dmamap_sync(9) is not functional on arm, > > then unmapped io should be disabled on arm unconditionally, using > > unmapped_buf_allowed. Why ahci(4) is special in this regard, leaving > > other controllers broken for arm ? > > I think this entire concept is wrong, and the fix should be in armv6 > busdma or pmap code. An unmapped page is, by definition, not cached. > The only way data becomes cached is because flags in a mapping indicated > the memory is cacheable. If we have data from unmapped pages in the > cache, that's a bug in the armv6 pmap implementation, I think.
I agree with the statement that the fix must be in busdma MD code, possibly with some cooperation with pmap code. On the other hand, I do not understand later claims. BIO unmapped attribute only means that bio does not carry a pointer to (some) mapping of the bio_ma pages. In other words, unmapped BIO does not imply globally unmapped page, and CPU cache might contain the lines from the BIO pages.
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