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April 4, 2021 11:34 am

Linus Torvalds Discusses Intel and AMD's New Proposals for Interrupt/Exception Handling

"AMD and Intel have both proposed better ways of doing interrupt and exception handling the last few months," reports LinuxReviews.org. Then they share this analysis Linus Torvalds posted on the Real World Technologies forum:"The AMD version is essentially "Fix known bugs in the exception handling definition". The Intel version is basically "Yeah, the protected mode 80286 exception handling was bad, then 386 made it odder with the 32-bit extensions, and then syscall/sysenter made everything worse, and then the x86-64 extensions introduced even more problems. So let's add a mode bit where all the crap goes away". In contrast, the AMD one is basically a minimal effort to fix actual fundamental problems with all that legacy-induced crap that are nasty to work around and that have caused issues... Both are valid on their own, and they are actually fairly independent. Honestly, the AMD paper looks like a quick "we haven't even finished thinking all the details through, but we know these parts were broken, so we might as well release this". I don't know how long it has been brewing, but judging by the "TBD" things in that paper, I think it's a "early rough draft"." In the article (shared by long-time Slashdot reader xiando), LinuxReviews.org summarizes the state of the conversation today:Torvalds went on to say that while AMD's proposed "quick fix" would be easier to implement for him and others operating system vendors, it's not ideal in the long run. Intel's proposal throws the entire existing interrupt descriptor table (IDT) delivery system under the bus so it can be replaced with what they call a new "FRED event delivery" system. Torvalds believes this is a better long-term solution... While the pros and cons of Intel and AMD's respective proposals for interrupt and event handling in future processors are worthy of discussion, it's in reality mostly up to Intel. They are the bigger and more powerful corporation. It is more likely than not that future processors from Intel will use their proposed Flexible Return and Event Delivery system. Their next generation processors won't, it will take years not months before consumer CPUs have the FRED technology. Remember, the above-mentioned technical document was published earlier this month [in March]. Things do not magically go from the drawing-board to store-shelves overnight. Intel isn't going to just hand the FRED technology over to AMD and help them implement it. We will likely see both move forward with their own proposals. Intel will have FRED and AMD will have Supervisor Entry Extensions until AMD, inevitably, adopts FRED or some form of it years down the line. They also note that Torvalds took issue with a poster arguing that microkernels are more secure than monolithic kernels like Linux."Bah, you're just parroting the usual party line that had absolutely no basis in reality and when you look into the details, doesn't actually hold up. It's all theory and handwaving and just repeating the same old FUD that was never actually really relevant."

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