[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-ia64-devel] Floating-point software assist (FPSWA) on Xen-ia64
> Subject: RE: [Xen-ia64-devel] Floating-point software assist > (FPSWA) on Xen-ia64 > > My speculation calling FPSWA within Xen will lead to > 1. Set FPSR accordingly to Domain kernel with Xen, and then > Save and restore domain FP registers before/after calling FPSWA in Xen > 2. ready to handle FP exceptions caused by FPSWA execution. > Note Domain application can't be trusted so it can likely > incure FP exception. Xen FP exception must also able to > distinguish exception source in order to unwind stack to > deliver to domain handler. Will one domain impact Xen stability? > 3. If domains doesn't got passed with FPSWA info, can its FP > handler able to handle exception delivered from Xen? > 4. FP opcode fetch must be performed within Xen (likely > within FPSWA) to get from domain application base on IIP. > TLB miss may likely happen and Xen can't handle it. > 5. Domain FPSWA usage time is charged to Xen in stead of itself > Xen may not able to handle above issues cleanly :-) You may be right, but it seems like the exact code that Linux uses should work, except that where Linux passes a signal to the application, Xen would instead reflect the fp assist fault. If I have a chance, I may prototype this just to see if it works... FPSWA isn't very high priority, but it would be nice to pass LTP if it is easy to fix. > To minic native behavior, can we provide a single physical > copy of FPSWA for whole system without coping for each new > domain created? That is, each domain will be given extra, > other than domain memory, physical block that contains the > same FPSWA. The memory is then exported to domains through > EFI descriptor or ELILO (Whatever the native method is) with > guest physical. For P2M, domains will map the FPSWA using > exported guest physical and then Xen will instead map with > the same machine physical block for all the domains. > > The assumption here is domains won't write to FPSWA to > clobber it otherwise Xen has to change mapping attribute. > Domain destroy may need to perform special handling on this > machine block, but it should be easy once we have page > reference count implemented. This can probably be done also but should wait until after the physical/machine memory work is redone as otherwise it might have to be done twice. If the easy solution (above) doesn't work, we should probably put it off until later. Dan _______________________________________________ Xen-ia64-devel mailing list Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-ia64-devel
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