[CCing the regression list, as it should be in the loop for regressions: https://docs.kernel.org/admin-guide/reporting-regressions.html] [TLDR: I'm adding this report to the list of tracked Linux kernel regressions; the text you find below is based on a few templates paragraphs you might have encountered already in similar form. See link in footer if these mails annoy you.] On 04.04.23 21:55, Dexuan-Linux Cui wrote: > On Tue, Mar 21, 2023 at 1:37 AM Petr Tesarik > <petrtesarik@xxxxxxxxxxxxxxx> wrote: >> >> From: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx> >> >> Explicit alignment and page alignment are used only to calculate >> the stride, not when checking actual slot physical address. >> >> Originally, only page alignment was implemented, and that worked, >> because the whole SWIOTLB is allocated on a page boundary, so >> aligning the start index was sufficient to ensure a page-aligned >> slot. >> >> When Christoph Hellwig added support for min_align_mask, the index >> could be incremented in the search loop, potentially finding an >> unaligned slot if minimum device alignment is between IO_TLB_SIZE >> and PAGE_SIZE. The bug could go unnoticed, because the slot size >> is 2 KiB, and the most common page size is 4 KiB, so there is no >> alignment value in between. >> >> IIUC the intention has been to find a slot that conforms to all >> alignment constraints: device minimum alignment, an explicit >> alignment (given as function parameter) and optionally page >> alignment (if allocation size is >= PAGE_SIZE). The most >> restrictive mask can be trivially computed with logical AND. The >> rest can stay. >> >> Fixes: 1f221a0d0dbf ("swiotlb: respect min_align_mask") >> Fixes: e81e99bacc9f ("swiotlb: Support aligned swiotlb buffers") >> Signed-off-by: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx> >> --- > [...] > > Hi Petr, this patch has gone into the mainline: > 0eee5ae10256 ("swiotlb: fix slot alignment checks") > > Somehow it breaks Linux VMs on Hyper-V: a regular VM with > swiotlb=force or a confidential VM (which uses swiotlb) fails to boot. > If I revert this patch, everything works fine. > > Cc'd Tianyu/Michael and the Hyper-V list. Thanks for the report. To be sure the issue doesn't fall through the cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression tracking bot: #regzbot ^introduced 0eee5ae10256 #regzbot title swiotlb: Linux VMs on Hyper-V broken #regzbot monitor: https://lore.kernel.org/all/20230405003549.GA21326@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ #regzbot ignore-activity This isn't a regression? This issue or a fix for it are already discussed somewhere else? It was fixed already? You want to clarify when the regression started to happen? Or point out I got the title or something else totally wrong? Then just reply and tell me -- ideally while also telling regzbot about it, as explained by the page listed in the footer of this mail. Developers: When fixing the issue, remember to add 'Link:' tags pointing to the report (the parent of this mail). See page linked in footer for details. Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) -- Everything you wanna know about Linux kernel regression tracking: https://linux-regtracking.leemhuis.info/about/#tldr That page also explains what to do if mails like this annoy you.
