riscv: Sparse-Memory/vmemmap out-of-bounds fix

riscv: Sparse-Memory/vmemmap out-of-bounds fix

[ Upstream commit a11dd49dcb9376776193e15641f84fcc1e5980c9 ]

Offset vmemmap so that the first page of vmemmap will be mapped
to the first page of physical memory in order to ensure that
vmemmap’s bounds will be respected during
pfn_to_page()/page_to_pfn() operations.
The conversion macros will produce correct SV39/48/57 addresses
for every possible/valid DRAM_BASE inside the physical memory limits.

v2:Address Alex's comments

Suggested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Dimitris Vlachos <dvlachos@ics.forth.gr>
Reported-by: Dimitris Vlachos <dvlachos@ics.forth.gr>
Closes: https://lore.kernel.org/linux-riscv/20240202135030.42265-1-csd4492@csd.uoc.gr
Fixes: d95f1a542c3d ("RISC-V: Implement sparsemem")
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240229191723.32779-1-dvlachos@ics.forth.gr
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>