Bug 103321
| Summary: | NPT page attribute support causes extreme slowdown | ||
|---|---|---|---|
| Product: | Virtualization | Reporter: | Sebastian Schütte (dracon) |
| Component: | kvm | Assignee: | virtualization_kvm |
| Status: | RESOLVED CODE_FIX | ||
| Severity: | normal | CC: | JimiJames.Bove |
| Priority: | P1 | ||
| Hardware: | x86-64 | ||
| OS: | Linux | ||
| Kernel Version: | 4.2-rc3+ | Subsystem: | |
| Regression: | No | Bisected commit-id: | |
| Attachments: |
dmesg
cpuinfo lspci |
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Created attachment 185511 [details]
cpuinfo
Created attachment 185521 [details]
lspci
Before discovering this bug page, I started a thread on the Arch forums before coming across a bug that's either the same one as this or something very similar. We've done some extra investigation over there. Here's a link: https://bbs.archlinux.org/viewtopic.php?pid=1574465 (In reply to Jimi from comment #3) > Before discovering this bug page, I started a thread on the Arch forums > before coming across a bug that's either the same one as this or something > very similar. We've done some extra investigation over there. Here's a link: > https://bbs.archlinux.org/viewtopic.php?pid=1574465 Er, that is, by "very similar" I mean the behavior. Obviously, they could have wildly different causes. As far as I am concerned, RC4 fixes the issue (should've marked it as fixed earlier) by reverting said commit. This change has also been backported to 4.2 stable about 2 weeks ago, AFAIK. Note that this bug is actually AMD specific and only affects CPUs with NPT support. Oh. Definitely not the same bug, then. Ours still isn't fixed and affects more than just AMD. |
Created attachment 185501 [details] dmesg For some reason the new NPT attribute support that has been introduced with 4.3-RC3 causes my VM to run awfully slow, I managed to track this issue to commit 3c2e7f7de3 ("KVM: SVM: use NPT page attributes"). The VM runs Win7 64bit via Qemu and uses PCI passthrough with several devices (primary GPU, USB, audio) on a AMD 970/SB950 based Asrock 970 EXTREME3 2.0 motherboard and an AMD Phenom II X6 CPU. There are no error/warning messages whatsoever, booting the VM takes several minutes just to get past the first boot screen.