Re: [Xen-devel] [PATCH v2 1/9] xen/vpci: introduce basic handlers to trap accesses to the PCI config space

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Roger Pau Monne [mailto:roger.pau@xxxxxxxxxx]
> Sent: 20 April 2017 16:18
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: konrad.wilk@xxxxxxxxxx; boris.ostrovsky@xxxxxxxxxx; Roger Pau Monne
> <roger.pau@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Subject: [PATCH v2 1/9] xen/vpci: introduce basic handlers to trap accesses
> to the PCI config space
> 
> This functionality is going to reside in vpci.c (and the corresponding vpci.h
> header), and should be arch-agnostic. The handlers introduced in this patch
> setup the basic functionality required in order to trap accesses to the PCI
> config space, and allow decoding the address and finding the corresponding
> handler that should handle the access (although no handlers are
> implemented).
> 
> Note that the traps to the PCI IO ports registers (0xcf8/0xcfc) are setup
> inside of a x86 HVM file, since that's not shared with other arches.
> 
> A new XEN_X86_EMU_VPCI x86 domain flag is added in order to signal Xen
> whether
> a domain should use the newly introduced vPCI handlers, this is only enabled
> for PVH Dom0 at the moment.
> 
> A very simple user-space test is also provided, so that the basic 
> functionality
> of the vPCI traps can be asserted. This has been proven quite helpful during
> development, since the logic to handle partial accesses or accesses that
> expand
> across multiple registers is not trivial.
> 
> The handlers for the registers are added to a red-black tree, that indexes
> them
> based on their offset. Since Xen needs to handle partial accesses to the
> registers and access that expand across multiple registers the logic in
> xen_vpci_{read/write} is kind of convoluted, I've tried to properly comment
> it
> in order to make it easier to understand.
> 

Since config space is not exactly huge, I'm wondering why you used an r-b tree 
rather than a direct map from register to handler?

  Paul
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