RE: [PATCH v4 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()
flat view
From: David Laight <hidden>
Date: 2021-02-01 17:39:52
From: Christopher M. Riedl
Sent: 01 February 2021 16:55
...
quoted
quoted
quoted
quoted
+ int i; \ + \ + unsafe_copy_from_user(buf, __f, ELF_NFPREG * sizeof(double), \ + label); \ + for (i = 0; i < ELF_NFPREG - 1; i++) \ + __t->thread.TS_FPR(i) = buf[i]; \ + __t->thread.fp_state.fpscr = buf[i]; \ +} while (0)On further reflection, since you immediately loop through the buffer why not just use user_access_begin() and unsafe_get_user() in the loop.Christophe had suggested this a few revisions ago as well. When I tried this approach, the signal handling performance took a pretty big hit: https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-October/219351.html I included some numbers on v3 as well but decided to drop the approach altogether for this one since it just didn't seem worth the hit.
Was that using unsafe_get_user (which relies on user_access_begin() having 'opened up' user accesses) or just get_user() that does it for every access? The former should be ok, the latter will be horrid. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)