> Von: David Laight [david.lai...@aculab.com] > Gesendet: Mittwoch, 25. Februar 2015 13:01 > An: Markus Stockhausen; linux-cry...@vger.kernel.org > Cc: linuxppc-dev@lists.ozlabs.org > Betreff: RE: [PATCH v1 1/3] SHA1 for PPC/SPE - assembler > > From: Markus Stockhausen > > [PATCH v1 1/3] SHA1 for PPC/SPE - assembler > > > > This is the assembler code for SHA1 implementation with > > the SIMD SPE instruction set. With the enhanced instruction > > set we can operate on 2 32 bit words in parallel. That helps > > reducing the time to calculate W16-W79. For increasing > > performance even more the assembler function can compute > > hashes for more than one 64 byte input block. > > > > The state of the used SPE registers is preserved via the > > stack so we can run from interrupt context > > Does the ppc use the same kind of delayed state save for the SPE > resisters that x86 uses (at least on the BSDs) for its FP (etc) regs. > > That would mean that the registers might contain values for > a different process, and that the cpu could receive an IPI > requesting they be written to the processes normal save area > so that they can be reloaded onto a different cpu.
Indeed SPE registers are lazy switched. enable_kernel_spe() will take care of that. Additionally I had some discussions about interrupt context and its limitations. So 1) I implemented register saving in all patches (see AES & SHA256). This is because I know which registers I will overwrite. One should remember that SPE registers are shared with normal registers. So no big impact to save 32 bit or 64 bit of the non-volatile PPC registers. 2) And used disabling of preemption. But in contrast to other crypto algorithm implementations only for reasonable time intervals Markus
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