On Thu, Jan 03, 2013 at 04:48:46PM -0800, Yinghai Lu wrote:
> Normal boot path on system with iommu support:
> swiotlb buffer will be allocated early at first and then try to initialize
> iommu, if iommu for intel or amd could setup properly, swiotlb buffer
> will be freed.
>
> The early allocating is with bootmem, and get panic when we try to use
> kdump with buffer above 4G only if swiotlb is enabled.
>
> because actually the kernel can go on without swiotlb, and use intel iommu.
>
> Try disable swiotlb if there is not enough ram for it.
>
> That is for kdump to use kernel above 4G.
>
> Suggested-by: Eric W. Biederman <ebied...@xmission.com>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Cc: Joerg Roedel <j...@8bytes.org>
> ---
> arch/x86/kernel/pci-swiotlb.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
> index 6c483ba..949ebfe 100644
> --- a/arch/x86/kernel/pci-swiotlb.c
> +++ b/arch/x86/kernel/pci-swiotlb.c
> @@ -6,6 +6,7 @@
> #include <linux/swiotlb.h>
> #include <linux/bootmem.h>
> #include <linux/dma-mapping.h>
> +#include <linux/memblock.h>
>
> #include <asm/iommu.h>
> #include <asm/swiotlb.h>
> @@ -50,6 +51,11 @@ static struct dma_map_ops swiotlb_dma_ops = {
> .dma_supported = NULL,
> };
>
> +static bool __init enough_mem_for_swiotlb(void)
> +{
> + /* do we have less than 1M RAM under 4G ? */
And why 1MB? The default size is 64MB.
> + return memblock_mem_size(1ULL<<(32-PAGE_SHIFT)) > (1ULL<<20);
> +}
> /*
> * pci_swiotlb_detect_override - set swiotlb to 1 if necessary
> *
> @@ -58,12 +64,12 @@ static struct dma_map_ops swiotlb_dma_ops = {
> */
> int __init pci_swiotlb_detect_override(void)
> {
> - int use_swiotlb = swiotlb | swiotlb_force;
> -
> if (swiotlb_force)
> swiotlb = 1;
> + else if (!enough_mem_for_swiotlb())
> + swiotlb = 0;
>
> - return use_swiotlb;
> + return swiotlb;
> }
> IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
> pci_xen_swiotlb_detect,
> @@ -78,7 +84,7 @@ int __init pci_swiotlb_detect_4gb(void)
> {
> /* don't initialize swiotlb if iommu=off (no_iommu=1) */
> #ifdef CONFIG_X86_64
> - if (!no_iommu && max_pfn > MAX_DMA32_PFN)
> + if (!no_iommu && max_pfn > MAX_DMA32_PFN && enough_mem_for_swiotlb())
> swiotlb = 1;
> #endif
> return swiotlb;
> --
> 1.7.10.4
>
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