On Thu, Aug 1, 2024 at 2:55 PM Marek Olšák <maraeo@xxxxxxxxx> wrote: > > On Thu, Aug 1, 2024, 03:37 Christian König <christian.koenig@xxxxxxx> wrote: >> >> Am 01.08.24 um 08:53 schrieb Marek Olšák: >> >> On Thu, Aug 1, 2024, 00:28 Khatri, Sunil <sukhatri@xxxxxxx> wrote: >>> >>> >>> On 8/1/2024 8:49 AM, Marek Olšák wrote: >>> >> + /* Header is at index 0, followed by num_nops - 1 NOP packet's */ >>> >> + for (i = 1; i < num_nop; i++) >>> >> + amdgpu_ring_write(ring, ring->funcs->nop); >>> > This loop should be removed. It's unnecessary CPU overhead and we >>> > should never get more than 0x3fff NOPs (maybe use BUG_ON). Leaving the >>> > whole packet body uninitialized is the fastest option. >>> That was the original intent to just move the WPTR for the no of nops >>> and tried too. Based on Christian inputs we should not let the nops packet >>> >>> as garbage or whatever was there originally as a threat/safety measure. >> >> >> It doesn't help safety. It can only be read by the GPU with kernel-level permissions. >> >> Initializing the packet body is useless and adds CPU overhead, especially with the 256 NOPs or so that we use for no reason. >> >> >> Not filling the remaining ring buffers with NOPs is a pretty clear NAK from my side. Leaving garbage in the ring buffer is not even remotely defensive. > > > What are you defending against? You know the ring is kernel-owned memory, right? This was pushed without any justification why you need to clear kernel-allocated memory with some constant number up to 30000 times per second that only the kernel can read. Marek
