Messages in this thread | | | From | Konrad Rzeszutek Wilk <> | Subject | [PATCH] Xen-SWIOTLB fixes (v4) for v3.7 | Date | Mon, 10 Sep 2012 15:45:57 -0400 |
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The original problem was: <begin> "if one boots a PV 64-bit guests with more than 4GB, the SWIOTLB [Xen] gets turned on - and 64MB of precious low-memory gets used." was totally bogus. The SWIOTLB that gets turned on is the *native* one - which does not exhaust any low-memory of the host. But it does eat up perfectly fine 64MB of the guest and never gets used.
So this patchset has some things I wanted to do for some time: [PATCH 01/10] xen/swiotlb: Simplify the logic.
Just so that next time I am not confused.
[PATCH 02/10] xen/swiotlb: With more than 4GB on 64-bit, disable the
and don't turn the *native* SWIOTLB on PV guests and waste those 64MB. <end>
The rest are exciting new patches - basically I want to emulate what IA64 does which is to turn on the SWIOTLB late in the bootup cycle. This means not using the alloc_bootmem and having a "late" variant to initialize SWIOTLB. There is some surgery in the SWIOTLB library: [PATCH 03/10] swiotlb: add the late swiotlb initialization function
to allow it to use an io_tlb passed in. Note: I hadn't tested this on IA64 and that is something I need to do.
And then the implementation in the Xen-SWIOTLB to use it: [PATCH 06/10] xen/swiotlb: Use the swiotlb_late_init_with_tbl to along with Xen PCI frontend to utilize it. [PATCH 07/10] xen/pcifront: Use Xen-SWIOTLB when initting if
The end result is that a PV guest can now dynamically(*) deal with PCI passthrough cards. I say "dynamically" b/c if one boots a PV guest with more than 3GB without using 'e820_hole' (or is it called 'e820_host' now?) the PCI subsystem won't be able to squeeze the BARs as they are RAM occupied. The workaround is to boot with 'e820_hole' or some new work where we manipulate at boot time the E820 to leave a nice big 1GB hole under 4G - and with all the work on the P2M tree that should be fairly easy actually.
Note: If one uses 'iommu=soft' on the Linux command line, the Xen-SWIOTLB still gets turned on.
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