On 8/23/22 10:51 AM, Yu Zhao wrote:
On Tue, Aug 23, 2022 at 11:25 AM Dongli Zhang dongli.zhang@oracle.com 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__%3B%21%21ACWV5... [2] https://urldefense.com/v3/__https://www.amazon.com/bestsellers/pc/300189__%3...
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/20220820012031.12859...
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