Ray Of Hope


interrupt path xen

interrupt generated by the hardware. based on the static interrupt routing configuration provided by ACPI table at boot time, the corresponding link is selected. Interrupt is delivered to IO-APIC. Most modern days IO-APICs converts interrupt to msi i.e memory writes to specfic address in LAPIC name space . Each interrupt is mapped to a specific […]


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secure Xen throught XSM

XSM (Xen Security Modules) is security frame provided by Xen to secure Xen domains. The implementation of the framework lies within FLASK (Flux Advanced Security Kernel) policies. XSM is the policy definition entity while FLASK is an enforcement engine. Aspects of domain(s) that can be controlled: 1) interaction between domains (domU vs domU / dom0 […]

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dynamic scheduler that can self-learn

I want to make scheduler dynamic so that it can give maximum performance based on the different workload by adjusting its configuration. To start with a simple case I have chosen runqueu configuration. Problem Statement : Consider a simple usecase: The person who doesn’t have much knowledge about the scheduler will have a hard time […]

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braindump- memory corruption

Linux kernel 3.10 has somewhat dubious use of __GFP_WAIT which is more recent kernel has been replaced __GFP_RECLAIM and __GFP_DIRECT_RECLAIM which are more sensible . I have been debugging a customer issue where AMD GPU passhtrough for S9050 card is causing XenServer host running 3.10 kernel to crash but XenServer 7.x Tech Preview release with […]

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XSM-Flask / Xen Credit-2 scheduler

Below are the links for my talk at XenSummit 2016 Toronto on 1) XSM/Flask current architecture, its shortcomings and new approach. 2) Credit-2 scheduler benchmarks and comparative results with Credit-1. Xen Credit-2 Scheduler Performance Benchmarks XSM Flask Let me know in case of any queries. Anshul Makkar anshul_makkar@justkernel.com

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Random host crash when running Xen + Braindump pvMMU.

Kernel crash call trace Apr 6 02:50:06 localhost kernel: [ 3107.388117] [] dump_stack+0x19/0x20 Apr 6 02:50:06 localhost kernel: [ 3107.388119] [] warn_slowpath_common+0x70/0xa0 Apr 6 02:50:06 localhost kernel: [ 3107.388122] [] warn_slowpath_null+0x1a/0x20 Apr 6 02:50:06 localhost kernel: [ 3107.388125] [] xen_mc_flush+0x177/0x190 Apr 6 02:50:06 localhost kernel: [ 3107.388128] [] __xen_pgd_pin+0x23c/0x290 Apr 6 02:50:06 localhost kernel: [ […]


Posted in debugging, Xen | 2 Comments »

Interrupt Path on Xen and on Baremetal system.

I was exploring an issue where qlogic device interrupt vector corresponding to a particular TX ring remained in masked state after the device comes up or is resetted. So the no packet transfer was possible on a port which was using that Tx queue and due to inaction, after some time this ports used to […]


Posted in Linux Kernel, virtualization, Xen | No Comments »

GPU Passthrough under ballooning + XEN and role of POD driver.

Its happening only in case HVM guest. I used Win 7 64 bit of reproducing the crash. This article is in continuation with the previous one where I saw a crash in RMRR region in case of GPU passthrough. To work around this problem I introduced a memory whole of 2 GB in the guest […]

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