[RFC PATCH 1/1] lib: sbi: fix dbtr shmem address handling

[Sergey Matyukevich]

Current debug triggers implementation in OpenSBI is accompanied by the
Linux kernel PoC code available on github, e.g. see the last two branches:

- https://github.com/hschauhan/riscv-linux/blob/linux-6.8-rc5-sdtrig
- https://github.com/hschauhan/riscv-linux/tree/sdtrig-virt

All implementation versions suggest a common way to pass shared memory
address to OpenSBI on RV32 and RV64 platforms. Shmem address is split
into two 32-bit parts and passed using two registers in SBI call.

This commit fixes shmem address handling for both RV32 and RV64. For
RV64 macro DBTR_SHMEM_MAKE_PHYS is updated to take into account both
high and low 32-bit parts of the passed shmem address. On RV32, M-mode
can only access the first 4GB of the physical address space. Macro
DBTR_SHMEM_MAKE_PHYS can be kept the same, though sbi_dbtr_setup_shmem
call should fail if the upper 32-bit part of the physical address is
not zero.

Suggested fix is for the kernel linux-6.8-rc5-sdtrig branch with the
modified sbi call in arch_smp_setup_sbi_shmem function:

simple snippet from the previous sdtrig-virt branch

:	ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_SETUP_SHMEM,
:			MEM_LO(shmem_pa), MEM_HI(shmem_pa), 0, 0, 0, 0);

instead of later version from linux-6.8-rc5-sdtrig

:	ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_SETUP_SHMEM,
:			(!MEM_LO(shmem_pa) ? 0xFFFFFFFFUL : MEM_LO(shmem_pa)),
:			(!MEM_HI(shmem_pa) ? 0xFFFFFFFFUL : MEM_HI(shmem_pa)),
:			 0, 0, 0, 0);

Fixes: 7f54527029d0 ("lib: sbi: fix DBTR_SHMEM_MAKE_PHYS for RV64")
Fixes: 97f234f15c96 ("lib: sbi: Introduce the SBI debug triggers extension support")

Signed-off-by: Sergey Matyukevich <geomatsi at gmail.com>
---
 lib/sbi/sbi_dbtr.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/sbi/sbi_dbtr.c b/lib/sbi/sbi_dbtr.c
index 9c92af6..8aa835f 100644
--- a/lib/sbi/sbi_dbtr.c
+++ b/lib/sbi/sbi_dbtr.c
@@ -47,13 +47,7 @@ static unsigned long hart_state_ptr_offset;
 	     _idx < _max;						\
 	     _idx++, _entry = ((_etype *)_base + _idx))
 
-#if __riscv_xlen == 64
-#define DBTR_SHMEM_MAKE_PHYS(_p_hi, _p_lo) (_p_lo)
-#elif __riscv_xlen == 32
 #define DBTR_SHMEM_MAKE_PHYS(_p_hi, _p_lo) (((u64)(_p_hi) << 32) | (_p_lo))
-#else
-#error "Undefined XLEN"
-#endif
 
 /* must call with hs != NULL */
 static inline bool sbi_dbtr_shmem_disabled(
@@ -277,6 +271,12 @@ int sbi_dbtr_setup_shmem(const struct sbi_domain *dom, unsigned long smode,
 	if (shmem_phys_lo & SBI_DBTR_SHMEM_ALIGN_MASK)
 		return SBI_ERR_INVALID_PARAM;
 
+#if __riscv_xlen == 32
+	 /* M-mode on RV32 can only access the first 4GB */
+	if (shmem_phys_hi)
+		return SBI_EINVALID_ADDR;
+#endif
+
 	if (dom && !sbi_domain_check_addr(dom,
 		  DBTR_SHMEM_MAKE_PHYS(shmem_phys_hi, shmem_phys_lo), smode,
 		  SBI_DOMAIN_READ | SBI_DOMAIN_WRITE))
-- 
2.45.2