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kinst: be explicit about trampoline placement

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The current implementation and comment was specific to amd64. Even
though in the case of kinst's supported architectures (RISC-V and ARM64)
VM_MIN_KERNEL_ADDRESS is equal to KERNBASE, it's better to be explicit.

Reviewed by:	markj
Approved by:	markj (mentor)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D40266
This commit is contained in:
Christos Margiolis 2023-05-25 23:40:46 +03:00
parent 5a7500dab9
commit 855ade9e72
1 changed files with 13 additions and 6 deletions
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19
sys/cddl/dev/kinst/trampoline.c
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@ -68,15 +68,22 @@ kinst_trampchunk_alloc(void)
sx_assert(&kinst_tramp_sx, SX_XLOCKED);
#ifdef __amd64__
/*
* Allocate virtual memory for the trampoline chunk. The returned
* address is saved in "trampaddr". To simplify population of
* trampolines, we follow the amd64 kernel's code model and allocate
* them above KERNBASE, i.e., in the top 2GB of the kernel's virtual
* address space. Trampolines must be executable so max_prot must
* include VM_PROT_EXECUTE.
* To simplify population of trampolines, we follow the amd64 kernel's
* code model and allocate them above KERNBASE, i.e., in the top 2GB of
* the kernel's virtual address space (not the case for other
* platforms).
*/
trampaddr = KERNBASE;
#else
trampaddr = VM_MIN_KERNEL_ADDRESS;
#endif
/*
* Allocate virtual memory for the trampoline chunk. The returned
* address is saved in "trampaddr". Trampolines must be executable so
* max_prot must include VM_PROT_EXECUTE.
*/
error = vm_map_find(kernel_map, NULL, 0, &trampaddr,
KINST_TRAMPCHUNK_SIZE, 0, VMFS_ANY_SPACE, VM_PROT_ALL, VM_PROT_ALL,
0);