RE: [Xen-devel] [PATCH] Misaligned IO reads

["Woller, Thomas" <thomas.woller@xxxxxxx>]

> This patch fixes a data corruption bug in hvm_pio_assist() of 
> xen/arch/x86/hvm/io.c.  When the OVERLAP flag is set and the 
> guest is running in real-mode regs->es is used in the 
> generation of the destination address passed to hvm_copy().  
> regs->es, however, has not been initialized and bad happens.  
> Since __vmread() must be called to obtain regs->es to remedy 
> the bug, this patch instead calls __vmread to obtain the 
> GUEST_LINEAR_ADDRESS which removes the need to check if the 
> guest is in real-mode and hence also the need to adjust addr. 
>  Since this block of code is executed so rarely, there is no 
> measurable performance impact using this fix for real or 
> protected mode guests.
Ross, should a __vmread be in an hvm specific function? Maybe I'm
missing something but a __vmread VT instruction will GP on an AMD SVM
platform.
Thanks for any clarification
Tom 





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