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marcan42's profile
Hector Martin
Hector Martin
Hector Martin
@marcan42

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Hector Martin

@marcan42

If it ain't broke, I'll fix it! I'm porting Linux to Apple Silicon Macs at @AsahiLinux. http://patreon.com/marcan  | http://github.com/sponsors/marcan 

Tokyo, Japan
marcan.st
Joined May 2009

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    1. Rich Felker‏ @RichFelker 11 May 2020
      • Report Tweet
      • Report NetzDG Violation
      Replying to @stevecheckoway @marcan42 @MissingClara

      See here for an account of how historically broken this stuff is on Linux and how the solutions are still prioritizing performance over getting it obviously safely right.https://lwn.net/Articles/786558/ …

      1 reply 0 retweets 2 likes
    2. Hector Martin‏ @marcan42 12 May 2020
      • Report Tweet
      • Report NetzDG Violation
      Replying to @RichFelker @stevecheckoway @MissingClara

      You don't have to tell me about drivers fucking up IOMMU mappings. That's how we owned the PS4. The solution isn't forcing bounce buffers on everything, it's better software frameworks for getting this right without just dumbly copying data.

      1 reply 0 retweets 3 likes
    3. Rich Felker‏ @RichFelker 12 May 2020
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      Replying to @marcan42 @stevecheckoway @MissingClara

      If final destination is userspace you can't. Other data may be in same page. Based on the LWN summary I posted it looks like they're doing bounce buffer mappings only for first/last partial pages...

      2 replies 0 retweets 0 likes
    4. 黒田 東彦 stan‏ @HarperMitchell 12 May 2020
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      Replying to @RichFelker @marcan42 and

      I've seen well-written DPDK drivers that manage to do a decent job

      1 reply 0 retweets 0 likes
    5. 黒田 東彦 stan‏ @HarperMitchell 12 May 2020
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      Replying to @HarperMitchell @RichFelker and

      Maybe there's something more fundamental I'm missing or being obtuse about

      1 reply 0 retweets 0 likes
    6. Hector Martin‏ @marcan42 12 May 2020
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      Replying to @HarperMitchell @RichFelker and

      The only thing you need to do is make sure all your DMA allocations are page-aligned and that you never store control structures not intended for the hardware in them. Any mapped pages are treated as untrusted data subject to change at any time.

      1 reply 0 retweets 3 likes
    7. 黒田 東彦 stan‏ @HarperMitchell 12 May 2020
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      Replying to @marcan42 @RichFelker and

      Right, also I don't see how the user/kernelspace distinction is relevant

      2 replies 0 retweets 0 likes
    8. Rich Felker‏ @RichFelker 12 May 2020
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      Replying to @HarperMitchell @marcan42 and

      Because the kernel can't control the alignment of buffers userspace passes to recv.

      2 replies 0 retweets 0 likes
    9. Hector Martin‏ @marcan42 12 May 2020
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      Replying to @RichFelker @HarperMitchell and

      Yes, you need to use bounce buffers for the first/last pages when that happens. That is expected. Userspace that wants performance needs to align.

      1 reply 0 retweets 1 like
    10. Hector Martin‏ @marcan42 12 May 2020
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      Replying to @marcan42 @RichFelker and

      There is a distinction here between e.g. standard socket APIs (you pretty much always need to copy anyway) and high performance stuff where userspace should know what it's doing. Same with graphics, ultimately GPU contexts can 1:1 map userspace contexts for stuff like games.

      1 reply 0 retweets 1 like
      Hector Martin‏ @marcan42 12 May 2020
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      Replying to @marcan42 @RichFelker and

      (and this is how it's done for secure game consoles, by the way, which are optimized for security *and* GPU perf)

      1:13 AM - 12 May 2020
      • 1 Like
      • 黒田 東彦 stan
      1 reply 0 retweets 1 like
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        1. 黒田 東彦 stan‏ @HarperMitchell 12 May 2020
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          Replying to @marcan42 @RichFelker and

          Also for cloud network adapters that use SRIOV

          1 reply 0 retweets 0 likes
        2. 黒田 東彦 stan‏ @HarperMitchell 12 May 2020
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          Replying to @HarperMitchell @marcan42 and

          Also optimized for both security and performance

          1 reply 0 retweets 0 likes
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