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Message-ID: <CAAhSdy06M8cP+mfvgHPMfEO8r0tO3C4YEJ80sTp2w4F1X75aTA@mail.gmail.com>
Date: Mon, 23 Jan 2023 16:56:14 +0530
From: Anup Patel <anup@...infault.org>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Jonathan Corbet <corbet@....net>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Conor Dooley <conor@...nel.org>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
Björn Töpel <bjorn@...nel.org>
Subject: Re: [PATCH resend v3] riscv: Allow to downgrade paging mode from the
command line
On Mon, Jan 23, 2023 at 4:21 PM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>
> Add 2 early command line parameters that allow to downgrade satp mode
> (using the same naming as x86):
> - "no5lvl": use a 4-level page table (down from sv57 to sv48)
> - "no4lvl": use a 3-level page table (down from sv57/sv48 to sv39)
>
> Note that going through the device tree to get the kernel command line
> works with ACPI too since the efi stub creates a device tree anyway with
> the command line.
>
> Also, as those params are treated very early in the boot process and we
> use standard device tree functions that may be kasan instrumented, we
> only enable them for !KASAN configurations.
>
> Reviewed-by: Björn Töpel <bjorn@...nel.org>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
Looks good to me.
Reviewed-by: Anup Patel <anup@...infault.org>
Regards,
Anup
> ---
>
> v3:
> - Massage commit log to make no4lvl clearer, as asked by Conor
> - Add a note to kernel-parameters.txt regarding the impossibility to use
> those parameters when KASAN is enabled, as suggested by Conor
> - Add RB from Björn
>
> v2:
> - Honor CMDLINE_EXTEND and CMDLINE_FORCE as noticed by Björn
>
> .../admin-guide/kernel-parameters.txt | 9 ++-
> arch/riscv/mm/init.c | 72 +++++++++++++++++--
> 2 files changed, 74 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6cfa6e3996cf..fd647412ec91 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3578,8 +3578,15 @@
> emulation library even if a 387 maths coprocessor
> is present.
>
> - no5lvl [X86-64] Disable 5-level paging mode. Forces
> + no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces
> + kernel to use 3-level paging instead.
> + Note: On RISC-V, this can't be used when KASAN is
> + enabled.
> +
> + no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces
> kernel to use 4-level paging instead.
> + Note: On RISC-V, this can't be used when KASAN is
> + enabled.
>
> nofsgsbase [X86] Disables FSGSBASE instructions.
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 478d6763a01a..10f99fa74368 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -746,17 +746,77 @@ static void __init disable_pgtable_l4(void)
> satp_mode = SATP_MODE_39;
> }
>
> +#ifndef CONFIG_KASAN
> +static __init bool match_noXlvl(const char *cmdline)
> +{
> + if (strstr(cmdline, "no5lvl")) {
> + disable_pgtable_l5();
> + } else if (strstr(cmdline, "no4lvl")) {
> + disable_pgtable_l5();
> + disable_pgtable_l4();
> + return true;
> + }
> +
> + return false;
> +}
> +
> +static int __init print_no4lvl(char *p)
> +{
> + pr_info("Disabled 4-level and 5-level paging");
> + return 0;
> +}
> +early_param("no4lvl", print_no4lvl);
> +
> +static int __init print_no5lvl(char *p)
> +{
> + pr_info("Disabled 5-level paging");
> + return 0;
> +}
> +early_param("no5lvl", print_no5lvl);
> +#endif
> +
> /*
> * 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
> * then read SATP to see if the configuration was taken into account
> * meaning sv48 is supported.
> */
> -static __init void set_satp_mode(void)
> +static __init void set_satp_mode(uintptr_t dtb_pa)
> {
> u64 identity_satp, hw_satp;
> uintptr_t set_satp_mode_pmd = ((unsigned long)set_satp_mode) & PMD_MASK;
> - bool check_l4 = false;
> +
> +#ifndef CONFIG_KASAN
> + /*
> + * The below fdt functions are kasan instrumented, since at this point
> + * there is no mapping for the kasan shadow memory, this can't be used
> + * when kasan is enabled.
> + */
> + int chosen_node;
> + unsigned int fdt_cmdline_size = 0;
> +
> + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
> + chosen_node = fdt_path_offset((void *)dtb_pa, "/chosen");
> + if (chosen_node >= 0) {
> + const char *fdt_cmdline;
> +
> + fdt_cmdline = fdt_getprop((void *)dtb_pa, chosen_node,
> + "bootargs", NULL);
> + if (fdt_cmdline) {
> + if (match_noXlvl(fdt_cmdline))
> + return;
> + fdt_cmdline_size = strlen(fdt_cmdline);
> + }
> + }
> + }
> +
> + if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
> + IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
> + fdt_cmdline_size == 0 /* CONFIG_CMDLINE_FALLBACK */) {
> + if (match_noXlvl(CONFIG_CMDLINE))
> + return;
> + }
> +#endif
>
> create_p4d_mapping(early_p4d,
> set_satp_mode_pmd, (uintptr_t)early_pud,
> @@ -775,7 +835,8 @@ static __init void set_satp_mode(void)
> retry:
> create_pgd_mapping(early_pg_dir,
> set_satp_mode_pmd,
> - check_l4 ? (uintptr_t)early_pud : (uintptr_t)early_p4d,
> + pgtable_l5_enabled ?
> + (uintptr_t)early_p4d : (uintptr_t)early_pud,
> PGDIR_SIZE, PAGE_TABLE);
>
> identity_satp = PFN_DOWN((uintptr_t)&early_pg_dir) | satp_mode;
> @@ -786,9 +847,8 @@ static __init void set_satp_mode(void)
> local_flush_tlb_all();
>
> if (hw_satp != identity_satp) {
> - if (!check_l4) {
> + if (pgtable_l5_enabled) {
> disable_pgtable_l5();
> - check_l4 = true;
> memset(early_pg_dir, 0, PAGE_SIZE);
> goto retry;
> }
> @@ -979,7 +1039,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> #endif
>
> #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
> - set_satp_mode();
> + set_satp_mode(dtb_pa);
> #endif
>
> kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
> --
> 2.37.2
>
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