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Ray Of Hope

Xen

Introduction of runqueue per cpupool for credit2 scheduler – Xen

Current infrastructure in Xen allows only a global runqueue flags that will be applicable to all the cpupools (schedulers, there is 1:1 correspondence between cpupools and scheduler instance running in a system). for eg. if we have selected configuration of runqueue as socket, then all the cpupools created will have the runqueue per cpupool. This […]

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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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Braindump + Segmentation and Paging And Xen

32 bit PV guest: guest kernel executes in ring 1 and guest user space executes in ring3. 64 bit PV guest: Guest kernel executes in ring 3 and guest user space also executes in ring 3. In 32 bit PV guest Xen used to use Segmentation based protection to protect Xen memory from being accessed […]

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RMRR region GPU passthough + xen

Today faced with a issue where one VM is assigned GPU via passthrough mode and other VM doesn’t have GPU assignement. If I swap the max and min dynamic memory assignment of both these VMs (changing the size of balloon for each VM), guest with GPU crashes after 2-3 iterations. E820 Map of Host: (XEN) […]

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multipage support for netback driver + Xen

Here are some of my learnings from my work on multipage support for netback driver. Learnings related to how we are making use of multi page and also how netback and netfron communicate. driver/xen/xen_probe.c keeps monitoring the backend and frontend states and calls the appropriate driver.otherend_changed(drivers/net/netfront or driver/net/netback) function. xenbus.c : static DEFINE_XENBUS_DRIVER(netback, , .probe […]

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Broadwell + Xen + Classic guest kernel + WRITE_FAULT + SMAP Violation.

Recently faced an issue where classic guest kernel (2.6.*) were faulting on Broadwell hardware. From the day 1 doubt was on SMAP feature that is exclusive to Broadwell but had to prove it. Approach: Compiled the guest kernel with instrumentation but can’t use it as the guest on Broadwell hangs just during reboot. (I compiled […]

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