On 8/23/22 10:51 AM, Yu Zhao wrote: > On Tue, Aug 23, 2022 at 11:25 AM Dongli Zhang <dongli.zhang@xxxxxxxxxx> wrote: >> >> Adding Robin, Yu and swiotlb list. > > Thanks. > >> There is an on-going discussion whether to revert this patch, because it breaks >> a corner case in MIPS > > I wouldn't call it a corner case. Cavium Octeon is the major platform > we use to test Debian MIPS ports [1], and 4 out of 5 best-selling > Wi-Fi routers are MIPS-based [2]. > > [1] https://urldefense.com/v3/__https://wiki.debian.org/MIPSPort__;!!ACWV5N9M2RV99hQ!NDVwU_XfPmfl_OSGxbroJXOjYmdrb-Vmbnx-zq0UIxkYNCetx4ZWdl6KlftLS9F5ORGT4t8F5YapMSSBiA$ > [2] https://urldefense.com/v3/__https://www.amazon.com/bestsellers/pc/300189__;!!ACWV5N9M2RV99hQ!NDVwU_XfPmfl_OSGxbroJXOjYmdrb-Vmbnx-zq0UIxkYNCetx4ZWdl6KlftLS9F5ORGT4t8F5YacDz0Zlg$ > >> when many kernel CONFIGs are not enabled (related to PCI >> and device). As a result, MIPS pre-allocates only PAGE_SIZE buffer as swiotlb. >> >> https://urldefense.com/v3/__https://lore.kernel.org/all/20220820012031.1285979-1-yuzhao@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!NDVwU_XfPmfl_OSGxbroJXOjYmdrb-Vmbnx-zq0UIxkYNCetx4ZWdl6KlftLS9F5ORGT4t8F5YbWJyEn2A$ >> >> However, the core idea of the patch is to panic on purpose if the swiotlb is >> configured with <1MB memory, in order to sync with the remap failure handler in >> swiotlb_init_remap(). >> >> Therefore, I am waiting for suggestion from Christoph whether (1) to revert this >> patch, or (2) enforce the restriction to disallow <1MB allocation. > > There are other archs (arm, ppc, riscv, s390, etc.) that call > swiotlb_init(). Have you verified them all? > The issue is not about swiotlb_init(). It is about swiotlb_adjust_size() where the 'default_nslabs' is configured to a very small value (e.g., equivalent to swiotlb=2). I do not see any arch can directly configure 'default_nslabs'. There are only two callers (archs) of swiotlb_adjust_size(): amd/sev and mips/cavium-octeon. About amd/sev, it uses at least IO_TLB_DEFAULT_SIZE so that there is not any issue. 244 size = total_mem * 6 / 100; 245 size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G); 246 swiotlb_adjust_size(size); In this case, only swiotlb=2 is allocated if PAGE_SIZE is 4K. Thank you very much! Dongli Zhang
