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Message-ID: <0d36f8a0-dff8-426a-a223-bfe344e84561@amd.com>
Date: Fri, 25 Oct 2024 11:41:48 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
x86@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>,
Nikunj A Dadhania <nikunj@....com>
Subject: Re: [PATCH v4 0/8] Provide support for RMPREAD and a segmented RMP
On 10/24/2024 12:11 AM, Tom Lendacky wrote:
> This series adds SEV-SNP support for a new instruction to read an RMP
> entry and for a segmented RMP table.
>
> The RMPREAD instruction is used to return information related to an RMP
> entry in an architecturally defined format.
>
> RMPREAD support is detected via CPUID 0x8000001f_EAX[21].
>
> Segmented RMP support is a new way of representing the layout of an RMP
> table. Initial RMP table support required the RMP table to be contiguous
> in memory. RMP accesses from a NUMA node on which the RMP doesn't reside
> can take longer than accesses from a NUMA node on which the RMP resides.
> Segmented RMP support allows the RMP entries to be located on the same
> node as the memory the RMP is covering, potentially reducing latency
> associated with accessing an RMP entry associated with the memory. Each
> RMP segment covers a specific range of system physical addresses.
>
> Segmented RMP support is detected and established via CPUID and MSRs.
>
> CPUID:
> - 0x8000001f_EAX[23]
> - Indicates support for segmented RMP
>
> - 0x80000025_EAX
> - [5:0] : Minimum supported RMP segment size
> - [11:6] : Maximum supported RMP segment size
>
> - 0x80000025_EBX
> - [9:0] : Number of cacheable RMP segment definitions
> - [10] : Indicates if the number of cacheable RMP segments is
> a hard limit
>
> MSR:
> - 0xc0010132 (RMP_BASE)
> - Is identical to current RMP support
>
> - 0xc0010133 (RMP_END)
> - Should be in reset state if segmented RMP support is active
>
> For kernels that do not support segmented RMP, being in reset
> state allows the kernel to disable SNP support if the non-segmented
> RMP has not been allocated.
>
> - 0xc0010136 (RMP_CFG)
> - [0] : Indicates if segmented RMP is enabled
> - [13:8] : Contains the size of memory covered by an RMP segment
> (expressed as a power of 2)
>
> The RMP segment size defined in the RMP_CFG MSR applies to all segments
> of the RMP. Therefore each RMP segment covers a specific range of system
> physical addresses. For example, if the RMP_CFG MSR value is 0x2401, then
> the RMP segment coverage value is 0x24 => 36, meaning the size of memory
> covered by an RMP segment is 64GB (1 << 36). So the first RMP segment
> covers physical addresses from 0 to 0xF_FFFF_FFFF, the second RMP segment
> covers physical addresses from 0x10_0000_0000 to 0x1F_FFFF_FFFF, etc.
>
> When a segmented RMP is enabled, RMP_BASE points to the RMP bookkeeping
> area as it does today (16K in size). However, instead of RMP entries
> beginning immediately after the bookkeeping area, there is a 4K RMP
> segment table. Each entry in the table is 8-bytes in size:
>
> - [19:0] : Mapped size (in GB)
> The mapped size can be less than the defined segment size.
> A value of zero, indicates that no RMP exists for the range
> of system physical addresses associated with this segment.
> [51:20] : Segment physical address
> This address is left shift 20-bits (or just masked when
> read) to form the physical address of the segment (1MB
> alignment).
>
> The series is based off of and tested against the tip tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master
>
> 94559bac4d40 ("Merge branch into tip/master: 'x86/sev'")
>
> ---
>
For the series:
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
- Neeraj
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