>From: Vineet Gupta <vgupta@xxxxxxxxxxxx> >Sent: Saturday, March 7, 2020 03:12 >To: Eugeniy Paltsev; linux-snps-arc@xxxxxxxxxxxxxxxxxxx >Cc: Alexey Brodkin; linux-kernel@xxxxxxxxxxxxxxx >Subject: Re: [PATCH v2 2/4] ARC: handle DSP presence in HW > >On 3/5/20 12:02 PM, Eugeniy Paltsev wrote: >> In case of DSP extension presence in HW some instructions >> (related to integer multiply, multiply-accumulate, and divide >> operation) executes on this DSP execution unit. So their >> execution will depend on dsp configuration register (DSP_CTRL) >> >> As we want these instructions to execute the same way regardless >> of DSP presence we need to set DSP_CTRL properly. However this >> register can be modified bu any usersace app therefore any >> usersace may break kernel execution. >> >> Fix that by configure DSP_CTRL in CPU early code and in IRQs >> entries. > > How about below .... > > "When DSP extensions are present, some of the regular integer instructions such as > DIV, MACD etc are executed in the DSP unit with semantics alterable by flags in > DSP_CTRL aux register. This register is writable by userspace and thus can > potentially affect corresponding instructions in kernel code, intentionally or > otherwise. So safegaurd kernel by effectively disabling DSP_CTRL upon bootup and > every entry to kernel. > > Do note that for this config we simply zero out the DSP_CTRL reg assuming > userspace doesn't really care about DSP. The next patch caters to the DSP aware > userspace which this actually saved/restored upon kernel entry." >From: Vineet Gupta <vgupta@xxxxxxxxxxxx> >Sent: Saturday, March 7, 2020 03:12 >To: Eugeniy Paltsev; linux-snps-arc@xxxxxxxxxxxxxxxxxxx >Cc: Alexey Brodkin; linux-kernel@xxxxxxxxxxxxxxx >Subject: Re: [PATCH v2 2/4] ARC: handle DSP presence in HW > >On 3/5/20 12:02 PM, Eugeniy Paltsev wrote: >> In case of DSP extension presence in HW some instructions >> (related to integer multiply, multiply-accumulate, and divide >> operation) executes on this DSP execution unit. So their >> execution will depend on dsp configuration register (DSP_CTRL) >> >> As we want these instructions to execute the same way regardless >> of DSP presence we need to set DSP_CTRL properly. However this >> register can be modified bu any usersace app therefore any >> usersace may break kernel execution. >> >> Fix that by configure DSP_CTRL in CPU early code and in IRQs >> entries. > > How about below .... > > "When DSP extensions are present, some of the regular integer instructions such as > DIV, MACD etc are executed in the DSP unit with semantics alterable by flags in > DSP_CTRL aux register. This register is writable by userspace and thus can > potentially affect corresponding instructions in kernel code, intentionally or > otherwise. So safegaurd kernel by effectively disabling DSP_CTRL upon bootup and > every entry to kernel. > > Do note that for this config we simply zero out the DSP_CTRL reg assuming > userspace doesn't really care about DSP. The next patch caters to the DSP aware > userspace which this actually saved/restored upon kernel entry." _______________________________________________ linux-snps-arc mailing list linux-snps-arc@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-snps-arc
