Re: [PATCH v3 6/8] x86/sev: Treat the contiguous RMP table as a single RMP segment

[Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>]

On 9/30/2024 8:52 PM, Tom Lendacky wrote:
> In preparation for support of a segmented RMP table, treat the contiguous
> RMP table as a segmented RMP table with a single segment covering all
> of memory. By treating a contiguous RMP table as a single segment, much
> of the code that initializes and accesses the RMP can be re-used.
> 
> Segmented RMP tables can have up to 512 segment entries. Each segment
> will have metadata associated with it to identify the segment location,
> the segment size, etc. The segment data and the physical address are used
> to determine the index of the segment within the table and then the RMP
> entry within the segment. For an actual segmented RMP table environment,
> much of the segment information will come from a configuration MSR. For
> the contiguous RMP, though, much of the information will be statically
> defined.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  arch/x86/virt/svm/sev.c | 195 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 176 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index 81e21d833cf0..ebfb924652f8 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -18,6 +18,7 @@
>  #include <linux/cpumask.h>
>  #include <linux/iommu.h>
>  #include <linux/amd-iommu.h>
> +#include <linux/nospec.h>
>  
>  #include <asm/sev.h>
>  #include <asm/processor.h>
> @@ -74,12 +75,42 @@ struct rmpentry_raw {
>   */
>  #define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
>  
> +/*
> + * For a non-segmented RMP table, use the maximum physical addressing as the
> + * segment size in order to always arrive at index 0 in the table.
> + */
> +#define RMPTABLE_NON_SEGMENTED_SHIFT	52
> +
> +struct rmp_segment_desc {
> +	struct rmpentry_raw *rmp_entry;
> +	u64 max_index;
> +	u64 size;
> +};
> +
> +/*
> + * Segmented RMP Table support.
> + *   - The segment size is used for two purposes:
> + *     - Identify the amount of memory covered by an RMP segment
> + *     - Quickly locate an RMP segment table entry for a physical address
> + *
> + *   - The RMP segment table contains pointers to an RMP table that covers
> + *     a specific portion of memory. There can be up to 512 8-byte entries,
> + *     one pages worth.
> + */
> +static struct rmp_segment_desc **rmp_segment_table __ro_after_init;
> +static unsigned int rst_max_index __ro_after_init = 512;
> +
> +static u64 rmp_segment_size_max;
> +static unsigned int rmp_segment_coverage_shift;
> +static unsigned long rmp_segment_coverage_size;
> +static unsigned long rmp_segment_coverage_mask;

rmp_segment_size_max is of type u64 and rmp_segment_coverage_size is 1 << 52
for single RMP segment. So, maybe use u64 for rmp_segment_coverage_size
and rmp_segment_coverage_mask also?


- Neeraj