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posted by martyb on Friday June 05 2020, @08:40AM   Printer-friendly
from the help-less,-please dept.

Linus Torvalds rejects 'beyond stupid' AWS-made Linux patch for Intel CPU Snoop attack

Linux kernel head Linus Torvalds has trashed a patch from Amazon Web Services (AWS) engineers that was aimed at mitigating the Snoop attack on Intel CPUs discovered by an AWS engineer earlier this year. [...] AWS engineer Pawel Wieczorkiewicz discovered a way to leak data from an Intel CPU's memory via its L1D cache, which sits in CPU cores, through 'bus snooping' – the cache updating operation that happens when data is modified in L1D.

In the wake of the disclosure, AWS engineer Balbir Singh proposed a patch for the Linux kernel for applications to be able to opt in to flush the L1D cache when a task is switched out. [...] The feature would allow applications on an opt-in basis to call prctl(2) to flush the L1D cache for a task once it leaves the CPU, assuming the hardware supports it.

But, as spotted by Phoronix, Torvalds believes the patch will allow applications that opt in to the patch to degrade CPU performance for other applications.

"Because it looks to me like this basically exports cache flushing instructions to user space, and gives processes a way to just say 'slow down anybody else I schedule with too'," wrote Torvalds yesterday. "In other words, from what I can tell, this takes the crazy 'Intel ships buggy CPU's and it causes problems for virtualization' code (which I didn't much care about), and turns it into 'anybody can opt in to this disease, and now it affects even people and CPU's that don't need it and configurations where it's completely pointless'."


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  • (Score: 2) by sjames on Saturday June 06 2020, @06:37PM (5 children)

    by sjames (2882) on Saturday June 06 2020, @06:37PM (#1004270) Journal

    Hanlon's razor has a tendency to come down to a judgement call, but to me it looks an awful lot like chinese walls to obscure a simple pay the competition to leave the market play, which would surely have triggered anti-trust investigations without the indirection. Of course, when Itanic sank, any such investigation became moot anyway.

    Honestly, Itanic's fate shouldn't have been that much of a surprise. After all, the 8086 was supposed to be an I/O co-processor for the much more baroque iAPX (not unlike channel I/O in an IBM) but the iAPX432 was such a lumbering Hippo that engineers noticed it was faster to offload the computation to the channel processors (8086).

    Basically, IBM, Intel, and then Microsoft more or less stumbled into relevance.

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  • (Score: 2) by Grishnakh on Saturday June 06 2020, @11:51PM (4 children)

    by Grishnakh (2831) on Saturday June 06 2020, @11:51PM (#1004368)

    but to me it looks an awful lot like chinese walls to obscure a simple pay the competition to leave the market play, which would surely have triggered anti-trust investigations

    Again, I do not understand what you're getting at here. Intel did not pay off AMD in any way: AMD released the x86-64. And Intel wasn't in competition with HP: they teamed up and worked on Itanium jointly. HP engineers were working with Intel engineers on the project.

    • (Score: 2) by sjames on Sunday June 07 2020, @02:24AM (3 children)

      by sjames (2882) on Sunday June 07 2020, @02:24AM (#1004393) Journal

      Intel wasn't in competition with HP, but if they didn't throw HP a bone, they would be when they got in to PA-RISC's market space. Or DEC's. You don't think it's a coincidence that 2 significant 64 bit CPUs just happened to exit the market when Intel wanted to introduce Itanic, do you?

      AMD shouldered it's way in later when they saw that Intel was in a tarpit with 64bit for the high end server market, giving them a chance to grab up the high end PC/workstation market with the 64bit x86 compatible CPU everyone really wanted..

      • (Score: 2) by Grishnakh on Sunday June 07 2020, @04:50PM (2 children)

        by Grishnakh (2831) on Sunday June 07 2020, @04:50PM (#1004549)

        You don't think it's a coincidence that 2 significant 64 bit CPUs just happened to exit the market when Intel wanted to introduce Itanic, do you?

        You need to go re-read your history. 2 significant 64-bit CPUs exited the market because the companies that owned them wanted to replace them with a newer, better one. It's as simple as that. You mention DEC. There was no DEC at this time. DEC died (probably due to a combination of mismanagement, other big-iron competitors, and the big-iron market drying up due to x86 servers), and pieces of it were bought up by both HP and Intel. HP and Intel decided to partner and work on Itanium. This wasn't some kind of conspiracy, it's what businesses do sometimes. It's no different than Chrysler and Mitsubishi forming Diamond Star Motors and building cars together. There's no law preventing businesses from forming partnerships.

        AMD shouldered it's way in later when they saw that Intel was in a tarpit with 64bit for the high end server market, giving them a chance to grab up the high end PC/workstation market with the 64bit x86 compatible CPU everyone really wanted..

        No, not really: Intel was trying to push the server market to Itanium and not getting much success because it didn't perform as well as promised and it cost a fortune. Intel didn't want there to be any cheap 64-bit CPUs on the market, and wanted the high profits that Itanium promised, and tried to act like a monopolist and force customers to use Itanium. HP partnered with them on this scheme. This is why they killed both PA-RISC and Alpha instead of continuing development of them. But Intel was arrogant and stupid, and somehow didn't think AMD would simply make their own 64-bit x86, so when they did, they were caught off-guard. They tried to downplay it for a while and convince customers they didn't really need it and that Itanic was better, but of course that didn't go very far. Basically, Intel showed a lot of hubris at the time, and it bit them in the ass.

        • (Score: 2) by sjames on Sunday June 07 2020, @06:57PM (1 child)

          by sjames (2882) on Sunday June 07 2020, @06:57PM (#1004585) Journal

          Your last paragraph actually summarized my position. HP and Intel did their best to kill competing processors so they could drive the price for 64 bit CPUS higher, but Itanic wasn't up to the task. AMD saw an opportunity to undercut them with a CPU that would definitely perform at least as well on existing 32 bit code as the current line of processors AND pave the way to 64 bit on the desktop.

          The HP-Intel partnership was a typical corporate business deal forged in Hell. Intel believed they could design and fab the processor, but needed HP to kill off competing CPUs. Both it's own PA-RISC and to buy up and shelf Alpha. The "technical collaboration" was mostly paper to wipe the smell of sulfur off of the deal.

          To this day, Intel is still gagging on the bitter pill of having to license x86-AMD64 from AMD.

          • (Score: 2) by Grishnakh on Sunday June 07 2020, @10:39PM

            by Grishnakh (2831) on Sunday June 07 2020, @10:39PM (#1004633)

            HP and Intel did their best to kill competing processors so they could drive the price for 64 bit CPUS higher, but Itanic wasn't up to the task. AMD saw an opportunity to undercut them with a CPU that would definitely perform at least as well on existing 32 bit code as the current line of processors AND pave the way to 64 bit on the desktop.

            Yes, I'd say this is accurate. But it wasn't some kind of secretive collusion or anything like that; DEC folded, the pieces went to HP and Intel, and they worked together (very much in the open) to develop and push Itanic as the new chip for big servers. Intel completely ignored customer calls for a 64-bit processor as computing needs were growing too large for the 4GB memory limit of the time, and tried to push PAE as a good-enough workaround. AMD saw the market demand and made a chip that the market wanted.