[SLOF] [RFC PATCH] pci-properties: Enforce all MMIO BARs to be 64K page aligned

[Nikunj A Dadhania]

Yongji Xie <xyjxie at linux.vnet.ibm.com> writes:

> QEMU may passthrough a pci device of which BARs are smaller than
> 64KB(PAGE_SIZE) to guest if all PCI MMIO BARs are page aligned in
> host. But these passthru-BARs' mmio page would be shared with other
> BARs in guest if guest doesn't support all PCI MMIO BARs to be page
> aligned. This would cause the pci-passthrough fail and mmio emulation
> happens in host.
>
> To solve this performance issue, this patch enforces the alignment
> of all MMIO BARs allocations to be at least 64K page aligned so that
> the mmio page of one BAR would not be shared with other BARs in guest.

So this would be basically hard-code (host page size 64k) page size. Is
there a better way to communicate this to the guest ?

We can pass host page size in the device tree and make this generic.

>
> Signed-off-by: Yongji Xie <xyjxie at linux.vnet.ibm.com>
> ---
>  slof/fs/pci-properties.fs |    5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/slof/fs/pci-properties.fs b/slof/fs/pci-properties.fs
> index da1d4fc..aebc7a7 100644
> --- a/slof/fs/pci-properties.fs
> +++ b/slof/fs/pci-properties.fs
> @@ -127,6 +127,7 @@
>  \ Setup a prefetchable 64bit BAR and return its size
>  : assign-mem64-bar ( bar-addr -- 8 )
>          dup pci-bar-size-mem64         \ fetch size
> +        10000 #aligned                  \ align size to minimum 64K (page size)
>          pci-next-mem                    \ var to change
>          assign-bar-value64              \ and set it all
>  ;
> @@ -134,6 +135,7 @@
>  \ Setup a prefetchable 32bit BAR and return its size
>  : assign-mem32-bar ( bar-addr -- 4 )
>          dup pci-bar-size-mem32          \ fetch size
> +        10000 #aligned                  \ align size to minimum 64K (page size)
>          pci-next-mem                    \ var to change
>          assign-bar-value32              \ and set it all
>  ;
> @@ -141,6 +143,7 @@
>  \ Setup a non-prefetchable 64bit BAR and return its size
>  : assign-mmio64-bar ( bar-addr -- 8 )
>          dup pci-bar-size-mem64          \ fetch size
> +        10000 #aligned                  \ align size to minimum 64K (page size)
>          pci-next-mmio                   \ var to change
>          assign-bar-value64              \ and set it all
>  ;
> @@ -148,6 +151,7 @@
>  \ Setup a non-prefetchable 32bit BAR and return its size
>  : assign-mmio32-bar ( bar-addr -- 4 )
>          dup pci-bar-size-mem32          \ fetch size
> +        10000 #aligned                  \ align size to minimum 64K (page size)
>          pci-next-mmio                   \ var to change
>          assign-bar-value32              \ and set it all
>  ;
> @@ -162,6 +166,7 @@
>  \ Setup an Expansion ROM bar
>  : assign-rom-bar ( bar-addr -- )
>          dup pci-bar-size-rom            \ fetch size
> +        10000 #aligned                  \ align size to minimum 64K (page size)
>          dup IF                          \ IF size > 0
>                  over >r                 \ | save bar addr for enable
>                  pci-next-mmio           \ | var to change
> -- 
> 1.7.9.5