Re: [PATCH] iommu/amd: Enforce 4k mapping for certain IOMMU data structures

[Joerg Roedel <joro@8bytes.org>]

Hi Suravee,

On Wed, Oct 28, 2020 at 11:18:24PM +0000, Suravee Suthikulpanit wrote:
> AMD IOMMU requires 4k-aligned pages for the event log, the PPR log,
> and the completion wait write-back regions. However, when allocating
> the pages, they could be part of large mapping (e.g. 2M) page.
> This causes #PF due to the SNP RMP hardware enforces the check based
> on the page level for these data structures.
> 
> So, fix by calling set_memory_4k() on the allocated pages.
> 
> Fixes: commit c69d89aff393 ("iommu/amd: Use 4K page for completion wait write-back semaphore")
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  drivers/iommu/amd/init.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 82e4af8f09bb..75dc30226a7c 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -29,6 +29,7 @@
>  #include <asm/iommu_table.h>
>  #include <asm/io_apic.h>
>  #include <asm/irq_remapping.h>
> +#include <asm/set_memory.h>
>  
>  #include <linux/crash_dump.h>
>  
> @@ -672,11 +673,22 @@ static void __init free_command_buffer(struct amd_iommu *iommu)
>  	free_pages((unsigned long)iommu->cmd_buf, get_order(CMD_BUFFER_SIZE));
>  }
>  
> +static void *__init iommu_alloc_4k_pages(gfp_t gfp, size_t size)
> +{
> +	void *buf;
> +	int order = get_order(size);
> +
> +	buf = (void *)__get_free_pages(gfp, order);
> +	if (!buf)
> +		return buf;
> +	return set_memory_4k((unsigned long)buf, (1 << order)) ? NULL : buf;
> +}
> +

Please make the 4k split only if SNP is actually enabled in the system.

Regards,

	Joerg