On 04.08.2022 16:28, Marek Marczykowski-Górecki wrote: > On Thu, Aug 04, 2022 at 04:21:01PM +0200, Jan Beulich wrote: >> On 04.08.2022 15:43, Marek Marczykowski-Górecki wrote: >>> I need to keep this structure somewhere DMA-reachable for the device (as >>> in - included in appropriate IOMMU context). Patch 8/10 is doing it. And >>> also, patch 8/10 is putting it together with other DMA-reachable >>> structures (not a separate page on its own). If I'd make it a separate >>> static variable (not part of that later struct), I'd need to reserve the >>> whole page for it - to guarantee no unrelated data lives on the same >>> (DMA-reachable) page. >>> >>> As for statically initializing it, if would require the whole >>> (multi-page DMA-reachable) thing living in .data, not .bss, so a bigger >>> binary (not a huge concern due to compression, but still). But more >>> importantly, I don't know how to do it in a readable way, and you have >>> complained about readability of initializer of this structure in v2. >>> >>>> That struct will be quite a bit less than a page's worth in size. >>> >>> See above - it cannot share page with unrelated Xen data. >> >> I have to admit that I'd see no issue if these lived side by side with >> e.g. other string literals. The more that the device is supposed to be >> exposed to Dom0 only anyway, and hence that'll be the only domain able >> to get at that data. > > Other string literals are fine. But for example `struct dbc` itself is > not. > See how it is combined with other data in patch 8. > >>>> If you build the file with -fshort-wchar, you may even be able to >>>> use easy to read string literals for the initializer. >>> >>> I can try, but I'm not exactly sure how to make readable UTF-16 >>> literals... >> >> L"Xen" looks sufficiently readable to me. We use this all over the >> place in the EFI interfacing code. > > Ok, I can try that. But given later adjustments, IIUC it will make the > whole 50+ pages structure land in .data. Is that okay?
No. I was actually expecting the piece of data we're talking about here to land in .rodata, and hence be re-usable at the same address for all devices. Hence my reference to string literals. Jan
