[PATCH 0/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[PATCH 0/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[Alexandre Ghiti]

+cc linux-mm since I'm struggling to know how bad is this issue and
if this should be picked for 6.1-rc8 or not.

I tested this fix on an Ubuntu kernel in sv39 mode without any issue
but the version without the fix seems to work fine too, either this is
not a real issue or I don't exercise the right thing to make it visible.

Any help appreciated!

Alexandre Ghiti (1):
  riscv: Fix P4D_SHIFT definition for 3-level page table mode

 arch/riscv/include/asm/pgtable-64.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.37.2

[PATCH 1/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[Alexandre Ghiti]

RISC-V kernels support 3,4,5-level page tables at runtime by folding
upper levels.

In case of a 3-level page table, PGDIR is folded into P4D which in turn
is folded into PUD: PGDIR_SHIFT value is correctly set to the same value
as PUD_SHIFT, but P4D_SHIFT is not, then any use of P4D_SHIFT will access
invalid address bits (all set to 1).

Fix this by dynamically defining P4D_SHIFT value, like we already do for
PGDIR_SHIFT.

Fixes: d10efa21a937 ("riscv: mm: Control p4d's folding by pgtable_l5_enabled")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/include/asm/pgtable-64.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
index dc42375c2357..42a042c0e13e 100644
--- a/arch/riscv/include/asm/pgtable-64.h
+++ b/arch/riscv/include/asm/pgtable-64.h
@@ -25,7 +25,11 @@ extern bool pgtable_l5_enabled;
 #define PGDIR_MASK      (~(PGDIR_SIZE - 1))
 
 /* p4d is folded into pgd in case of 4-level page table */
-#define P4D_SHIFT      39
+#define P4D_SHIFT_L3   30
+#define P4D_SHIFT_L4   39
+#define P4D_SHIFT_L5   39
+#define P4D_SHIFT      (pgtable_l5_enabled ? P4D_SHIFT_L5 : \
+		(pgtable_l4_enabled ? P4D_SHIFT_L4 : P4D_SHIFT_L3))
 #define P4D_SIZE       (_AC(1, UL) << P4D_SHIFT)
 #define P4D_MASK       (~(P4D_SIZE - 1))
 
-- 
2.37.2

Re: [PATCH 1/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[Palmer Dabbelt]

On Thu, 01 Dec 2022 05:51:28 PST (-0800), alexghiti@rivosinc.com wrote:
> RISC-V kernels support 3,4,5-level page tables at runtime by folding
> upper levels.
>
> In case of a 3-level page table, PGDIR is folded into P4D which in turn
> is folded into PUD: PGDIR_SHIFT value is correctly set to the same value
> as PUD_SHIFT, but P4D_SHIFT is not, then any use of P4D_SHIFT will access
> invalid address bits (all set to 1).
>
> Fix this by dynamically defining P4D_SHIFT value, like we already do for
> PGDIR_SHIFT.
>
> Fixes: d10efa21a937 ("riscv: mm: Control p4d's folding by pgtable_l5_enabled")
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  arch/riscv/include/asm/pgtable-64.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index dc42375c2357..42a042c0e13e 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -25,7 +25,11 @@ extern bool pgtable_l5_enabled;
>  #define PGDIR_MASK      (~(PGDIR_SIZE - 1))
>
>  /* p4d is folded into pgd in case of 4-level page table */
> -#define P4D_SHIFT      39
> +#define P4D_SHIFT_L3   30
> +#define P4D_SHIFT_L4   39
> +#define P4D_SHIFT_L5   39
> +#define P4D_SHIFT      (pgtable_l5_enabled ? P4D_SHIFT_L5 : \
> +		(pgtable_l4_enabled ? P4D_SHIFT_L4 : P4D_SHIFT_L3))
>  #define P4D_SIZE       (_AC(1, UL) << P4D_SHIFT)
>  #define P4D_MASK       (~(P4D_SIZE - 1))

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>

Too late for this week, but if someone's got a concrete regression then 
I'm happy to take it next week.  Otherwise it'll end up on for-next, 
it'll be backported anyway but this way it'll have a touch more time.

Thanks!

Re: [PATCH 0/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[Palmer Dabbelt]

On Thu, 1 Dec 2022 14:51:27 +0100, Alexandre Ghiti wrote:
> +cc linux-mm since I'm struggling to know how bad is this issue and
> if this should be picked for 6.1-rc8 or not.
> 
> I tested this fix on an Ubuntu kernel in sv39 mode without any issue
> but the version without the fix seems to work fine too, either this is
> not a real issue or I don't exercise the right thing to make it visible.
> 
> [...]

Applied, thanks!

[1/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode
      https://git.kernel.org/palmer/c/71fc3621efc3

Best regards,
-- 
Palmer Dabbelt <palmer@rivosinc.com>

Re: [PATCH 0/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Thu,  1 Dec 2022 14:51:27 +0100 you wrote:
> +cc linux-mm since I'm struggling to know how bad is this issue and
> if this should be picked for 6.1-rc8 or not.
> 
> I tested this fix on an Ubuntu kernel in sv39 mode without any issue
> but the version without the fix seems to work fine too, either this is
> not a real issue or I don't exercise the right thing to make it visible.
> 
> [...]

Here is the summary with links:
  - [1/1] riscv: Fix P4D_SHIFT definition for 3-level page table mode
    https://git.kernel.org/riscv/c/71fc3621efc3

You are awesome, thank you!
-- 
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