Re: [edk2-devel] [edk2-platforms][PATCH V1 02/20] StandaloneMmPkg: Allocate and initialise SP stack from internal memory

["Chris Fernald" <chris.fernald@outlook.com>]

Would it be possible to make the stack size configurable in a way that 
doesn't require an silicon/platform vendor to customize the assembly 
code? Perhaps through a fixed PCD if its not problematic to do so with 
the .space directive.

Thanks,

Chris

On 7/11/2023 7:36 AM, Nishant Sharma wrote:
> From: Achin Gupta <achin.gupta@arm.com>
>
> This patch removes the dependency on the SPM to allocate and initialise
> stack memory for the StMM SP. This is done by reserving 8K worth of memory
> in the StMM image at a page aligned address in the data section. Then,
> instead of jumping directly to the C entrypoint, an assembler entrypoint is
> invoked. This entrypoint locates the stack memory, changes its permissions
> using FF-A ABIs, sets the stack pointer and invokes the C entrypoint.
>
> Signed-off-by: Achin Gupta <achin.gupta@arm.com>
> Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
> ---
>   StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreEntryPoint.inf   |  1 +
>   StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/StandaloneMmCoreEntryPoint.c |  2 +-
>   StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/AArch64/ModuleEntryPoint.S   | 68 ++++++++++++++++++++
>   3 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreEntryPoint.inf b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreEntryPoint.inf
> index dc6d3d859911..10fafa43ce59 100644
> --- a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreEntryPoint.inf
> +++ b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreEntryPoint.inf
> @@ -25,6 +25,7 @@
>     Arm/StandaloneMmCoreEntryPoint.c
>     Arm/SetPermissions.c
>     Arm/CreateHobList.c
> +  Arm/AArch64/ModuleEntryPoint.S
>   
>   [Sources.X64]
>     X64/StandaloneMmCoreEntryPoint.c
> diff --git a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/StandaloneMmCoreEntryPoint.c b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/StandaloneMmCoreEntryPoint.c
> index 5dd1d9747995..ce867fe85158 100644
> --- a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/StandaloneMmCoreEntryPoint.c
> +++ b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/StandaloneMmCoreEntryPoint.c
> @@ -316,7 +316,7 @@ InitArmSvcArgs (
>   **/
>   VOID
>   EFIAPI
> -_ModuleEntryPoint (
> +ModuleEntryPoint (
>     IN VOID    *SharedBufAddress,
>     IN UINT64  SharedBufSize,
>     IN UINT64  cookie1,
> diff --git a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/AArch64/ModuleEntryPoint.S b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/AArch64/ModuleEntryPoint.S
> new file mode 100644
> index 000000000000..174bc83ebd64
> --- /dev/null
> +++ b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/Arm/AArch64/ModuleEntryPoint.S
> @@ -0,0 +1,68 @@
> +//
> +//  Copyright (c) 2023, ARM Limited. All rights reserved.
> +//
> +//  SPDX-License-Identifier: BSD-2-Clause-Patent
> +//
> +//
> +
> +#include <AsmMacroIoLibV8.h>
> +
> +#define FFA_DATA_RW 0x1
> +
> +.align 12
> +StackBase:
> +.space 8192
> +StackEnd:
> +
> +.macro FfaMemPermSet start:req end:req perm:req
> +adrp x29, \start
> +add x29, x29, :lo12: \start
> +
> +adrp x30, \end
> +add x30, x30, :lo12:\end
> +
> +/* x30 = end - begin */
> +sub x30, x30, x29
> +/* x28 = x30 >> 12 (number of pages) */
> +mov x28, #12
> +lsrv x28, x30, x28
> +
> +mov w0, #0x89
> +movk w0, #0x8400, lsl #16
> +mov x1, x29
> +mov x2, x28
> +mov w3, #\perm
> +
> +svc #0
> +
> +mov w1, #0x61
> +movk w1, #0x8400, lsl #16
> +cmp w1, w0
> +b.ne .
> +.endm
> +
> +  ASM_FUNC(_ModuleEntryPoint)
> +MOV32 (w8, FixedPcdGet32(PcdFfaEnable))
> +  cbz w8, FfaNotEnabled
> +  // Stash boot information registers from the SPMC
> +  mov x8, x0
> +  mov x9, x1
> +  mov x10, x2
> +  mov x11, x3
> +
> +  // Set the correct permissions on stack memory
> +  FfaMemPermSet StackBase StackEnd FFA_DATA_RW
> +
> +  // Initialise SP
> +  adr x0, StackEnd
> +  mov   sp, x0
> +
> +  // Restore boot information registers from the SPMC
> +  mov x0, x8
> +  mov x1, x9
> +  mov x2, x10
> +  mov x3, x11
> +
> +  // Invoke the C entrypoint
> +  FfaNotEnabled:
> +  b     ModuleEntryPoint