Re: [Xen-devel] [PATCH v2 1/5] hvmloader: Correct bug in low mmio region accounting

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 18 Jun 2013, George Dunlap wrote:
> When deciding whether to map a device in low MMIO space (<4GiB),
> hvmloader compares it with "mmio_left", which is set to the size of
> the low MMIO range (pci_mem_end - pci_mem_start).  However, even if it
> does map a device in high MMIO space, it still removes the size of its
> BAR from mmio_left.
> 
> This patch first changes the name of this variable to "low_mmio_left"
> to distinguish it from generic MMIO, and corrects the logic to only
> subtract the size of the BAR for devices maped in the low MMIO region.
> 
> Also make low_mmio_left unsigned, and don't allow it to go negative.
> Since its main use is to be compared to a 64-bit unsigned int, this
> may have undefined (and in practice almost certainly incorrect)
> results.  Not subtracting is OK because if there's not enough room, it
> won't actually be mapped.
> 
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> CC: Hanweidong <hanweidong@xxxxxxxxxx>
> ---
>  tools/firmware/hvmloader/pci.c |   10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/firmware/hvmloader/pci.c b/tools/firmware/hvmloader/pci.c
> index c78d4d3..8691a19 100644
> --- a/tools/firmware/hvmloader/pci.c
> +++ b/tools/firmware/hvmloader/pci.c
> @@ -38,11 +38,10 @@ void pci_setup(void)
>  {
>      uint8_t is_64bar, using_64bar, bar64_relocate = 0;
>      uint32_t devfn, bar_reg, cmd, bar_data, bar_data_upper;
> -    uint64_t base, bar_sz, bar_sz_upper, mmio_total = 0;
> +    uint64_t base, bar_sz, bar_sz_upper, low_mmio_left, mmio_total = 0;
>      uint32_t vga_devfn = 256;
>      uint16_t class, vendor_id, device_id;
>      unsigned int bar, pin, link, isa_irq;
> -    int64_t mmio_left;
>  
>      /* Resources assignable to PCI devices via BARs. */
>      struct resource {
> @@ -244,7 +243,7 @@ void pci_setup(void)
>      io_resource.base = 0xc000;
>      io_resource.max = 0x10000;
>  
> -    mmio_left = pci_mem_end - pci_mem_start;
> +    low_mmio_left = pci_mem_end - pci_mem_start;
>  
>      /* Assign iomem and ioport resources in descending order of size. */
>      for ( i = 0; i < nr_bars; i++ )
> @@ -253,7 +252,7 @@ void pci_setup(void)
>          bar_reg = bars[i].bar_reg;
>          bar_sz  = bars[i].bar_sz;
>  
> -        using_64bar = bars[i].is_64bar && bar64_relocate && (mmio_left < 
> bar_sz);
> +        using_64bar = bars[i].is_64bar && bar64_relocate && (low_mmio_left < 
> bar_sz);
>          bar_data = pci_readl(devfn, bar_reg);
>  
>          if ( (bar_data & PCI_BASE_ADDRESS_SPACE) ==
> @@ -273,9 +272,10 @@ void pci_setup(void)
>              } 
>              else {
>                  resource = &mem_resource;
> +                if ( bar_sz <= low_mmio_left )
> +                    low_mmio_left -= bar_sz;

Why do you need this check? Isn't the above if(using_64bar && (bar_sz >
PCI_MIN_BIG_BAR_SIZE)) enough?


>                  bar_data &= ~PCI_BASE_ADDRESS_MEM_MASK;
>              }
> -            mmio_left -= bar_sz;
>          }
>          else
>          {
> -- 
> 1.7.9.5
> 

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