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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 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.

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  • (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.