riscv: Fix config KASAN && SPARSEMEM && !SPARSE_VMEMMAP

stable inclusion
from stable-v5.10.104
commit 7211aab2881b0a8b6a002ec2eb341b2d3cb9f003
bugzilla: https://gitee.com/openeuler/kernel/issues/I56XAC

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7211aab2881b0a8b6a002ec2eb341b2d3cb9f003

--------------------------------

commit a3d32803 upstream.

In order to get the pfn of a struct page* when sparsemem is enabled
without vmemmap, the mem_section structures need to be initialized which
happens in sparse_init.

But kasan_early_init calls pfn_to_page way before sparse_init is called,
which then tries to dereference a null mem_section pointer.

Fix this by removing the usage of this function in kasan_early_init.

Fixes: 8ad8b727 ("riscv: Add KASAN support")
Signed-off-by: NAlexandre Ghiti <alexandre.ghiti@canonical.com>
Cc: stable@vger.kernel.org
Signed-off-by: NPalmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/riscv/mm/kasan_init.c

@@ -21,8 +21,7 @@ asmlinkage void __init kasan_early_init(void)
 
 	for (i = 0; i < PTRS_PER_PTE; ++i)
 		set_pte(kasan_early_shadow_pte + i,
-			mk_pte(virt_to_page(kasan_early_shadow_page),
-			       PAGE_KERNEL));
+			pfn_pte(virt_to_pfn(kasan_early_shadow_page), PAGE_KERNEL));
 
 	for (i = 0; i < PTRS_PER_PMD; ++i)
 		set_pmd(kasan_early_shadow_pmd + i,