Re: [PATCH V2] riscv: mm: Fixup no5lvl failure when vaddr is invalid

[fangyu.yu@linux.alibaba.com]

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>From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>
>
>Unlike no4lvl, no5lvl still continues detect satp, which
>requires va=pa mapping. When pa=0x800000000000, no5lvl
>would fail in Sv48 mode due to an illegal VA value of
>0x800000000000.
>
>So, prevent detecting the satp flow for no5lvl, when
>vaddr is invalid. Add the is_vaddr_valid() function for
>checking.
>
>Fixes: 26e7aacb83df ("riscv: Allow to downgrade paging mode from the command line")
>Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
>Cc: Björn Töpel <bjorn@rivosinc.com>
>Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
>---
>Changelog:
>
>v2:
> - Use is_vaddr_valid() instead of simple return.
> - Don't change the original no5lvl code logic.
>
>v1:
>https://lore.kernel.org/linux-riscv/20260118145441.291302-1-guoren@kernel.org/
>---
> arch/riscv/mm/init.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
>diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>index addb8a9305be..bfea9f73e703 100644
>--- a/arch/riscv/mm/init.c
>+++ b/arch/riscv/mm/init.c
>@@ -852,6 +852,27 @@ static void __init set_mmap_rnd_bits_max(void)
> 	mmap_rnd_bits_max = MMAP_VA_BITS - PAGE_SHIFT - 3;
> }
> 
>+static bool __init is_vaddr_valid(unsigned long va)
>+{
>+	unsigned long up = 0;
>+
>+	switch (satp_mode) {
>+	case SATP_MODE_39:
>+		up = 1UL << 38;
>+		break;
>+	case SATP_MODE_48:
>+		up = 1UL << 47;
>+		break;
>+	case SATP_MODE_57:
>+		up = 1UL << 56;
>+		break;
>+	default:
>+		return false;
>+	}
>+
>+	return (va < up) || (va >= (ULONG_MAX - up + 1));
>+}
>+
> /*
>  * There is a simple way to determine if 4-level is supported by the
>  * underlying hardware: establish 1:1 mapping in 4-level page table mode
>@@ -893,6 +914,9 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
> 			   set_satp_mode_pmd + PMD_SIZE,
> 			   PMD_SIZE, PAGE_KERNEL_EXEC);
> retry:
>+	if (!is_vaddr_valid(set_satp_mode_pmd))
>+		goto out;
>+
> 	create_pgd_mapping(early_pg_dir,
> 			   set_satp_mode_pmd,
> 			   pgtable_l5_enabled ?
>@@ -915,6 +939,7 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
> 		disable_pgtable_l4();
> 	}
> 
>+out:
> 	memset(early_pg_dir, 0, PAGE_SIZE);
> 	memset(early_p4d, 0, PAGE_SIZE);
> 	memset(early_pud, 0, PAGE_SIZE);
>--
>2.40.1

Tested on hardware where DRAM/PA starts at 0x800000000000.  With "no5lvl"
on the kernel command line, the kernel boots successfully after this patch.

Tested-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Thanks,
Fangyu


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