diff mbox series

riscv: toggle mmu_enabled flag in a precise manner

Message ID 20201201090023.2852-1-vitaly.wool@konsulko.com (mailing list archive)
State New, archived
Headers show
Series riscv: toggle mmu_enabled flag in a precise manner | expand

Commit Message

Vitaly Wool Dec. 1, 2020, 9 a.m. UTC 
From: Vitaly Wool <vitaly.wool@konsulko.com>

Cuurently mmu_enabled flag is set to true way later than the actual
MMU enablement takes place. This leads to hard-to-track races in
e. g. SBI earlycon initialization taking wrong path configuring
fixmap.

To fix that, move mmu_enabled toggling to head.S and rename it to
_mmu_enabled to avoid possible name clashes since it's not a static
variable any more.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
---
 arch/riscv/kernel/head.S |  9 +++++++++
 arch/riscv/mm/init.c     | 13 +++++--------
 2 files changed, 14 insertions(+), 8 deletions(-)

Comments

Atish Patra Dec. 1, 2020, 5:40 p.m. UTC | #1 
On Tue, Dec 1, 2020 at 1:01 AM <vitaly.wool@konsulko.com> wrote:
>
> From: Vitaly Wool <vitaly.wool@konsulko.com>
>
> Cuurently mmu_enabled flag is set to true way later than the actual
> MMU enablement takes place. This leads to hard-to-track races in
> e. g. SBI earlycon initialization taking wrong path configuring
> fixmap.
>

This code path is significantly changed in 5.10-rcX with UEFI series.
https://patchwork.kernel.org/project/linux-riscv/patch/20200917223716.2300238-4-atish.patra@wdc.com/

Can you check if you can still reproduce the issue you were seeing
with the latest upstream kernel ?
If yes, please share the steps to reproduce the issue.

> To fix that, move mmu_enabled toggling to head.S and rename it to
> _mmu_enabled to avoid possible name clashes since it's not a static
> variable any more.
>
> Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
> ---
>  arch/riscv/kernel/head.S |  9 +++++++++
>  arch/riscv/mm/init.c     | 13 +++++--------
>  2 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 0a4e81b8dc79..33cd57285be3 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -248,6 +248,10 @@ clear_bss_done:
>         call relocate
>  #endif /* CONFIG_MMU */
>
> +       la a0, _mmu_enabled
> +       li a1, 1
> +       sw a1, (a0)
> +
>         call setup_trap_vector
>         /* Restore C environment */
>         la tp, init_task
> @@ -370,6 +374,11 @@ ENTRY(reset_regs)
>  END(reset_regs)
>  #endif /* CONFIG_RISCV_M_MODE */
>
> +.section ".data"
> +       .global _mmu_enabled
> +_mmu_enabled:
> +       .word 0
> +
>  __PAGE_ALIGNED_BSS
>         /* Empty zero page */
>         .balign PAGE_SIZE
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 787c75f751a5..4038be635e25 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -211,7 +211,7 @@ EXPORT_SYMBOL(pfn_base);
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
>  pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
>  pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> -static bool mmu_enabled;
> +extern bool _mmu_enabled;
>
>  #define MAX_EARLY_MAPPING_SIZE SZ_128M
>
> @@ -236,7 +236,7 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
>
>  static pte_t *__init get_pte_virt(phys_addr_t pa)
>  {
> -       if (mmu_enabled) {
> +       if (_mmu_enabled) {
>                 clear_fixmap(FIX_PTE);
>                 return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
>         } else {
> @@ -250,7 +250,7 @@ static phys_addr_t __init alloc_pte(uintptr_t va)
>          * We only create PMD or PGD early mappings so we
>          * should never reach here with MMU disabled.
>          */
> -       BUG_ON(!mmu_enabled);
> +       BUG_ON(!_mmu_enabled);
>
>         return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>  }
> @@ -281,7 +281,7 @@ pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
>
>  static pmd_t *__init get_pmd_virt(phys_addr_t pa)
>  {
> -       if (mmu_enabled) {
> +       if (_mmu_enabled) {
>                 clear_fixmap(FIX_PMD);
>                 return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
>         } else {
> @@ -293,7 +293,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>  {
>         uintptr_t pmd_num;
>
> -       if (mmu_enabled)
> +       if (_mmu_enabled)
>                 return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>
>         pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> @@ -467,9 +467,6 @@ static void __init setup_vm_final(void)
>         phys_addr_t pa, start, end;
>         struct memblock_region *reg;
>
> -       /* Set mmu_enabled flag */
> -       mmu_enabled = true;
> -
>         /* Setup swapper PGD for fixmap */
>         create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
>                            __pa_symbol(fixmap_pgd_next),
> --
> 2.20.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
Vitaly Wool Dec. 1, 2020, 8:27 p.m. UTC | #2 
On Tue, Dec 1, 2020 at 6:40 PM Atish Patra <atishp@atishpatra.org> wrote:
>
> On Tue, Dec 1, 2020 at 1:01 AM <vitaly.wool@konsulko.com> wrote:
> >
> > From: Vitaly Wool <vitaly.wool@konsulko.com>
> >
> > Cuurently mmu_enabled flag is set to true way later than the actual
> > MMU enablement takes place. This leads to hard-to-track races in
> > e. g. SBI earlycon initialization taking wrong path configuring
> > fixmap.
> >
>
> This code path is significantly changed in 5.10-rcX with UEFI series.
> https://patchwork.kernel.org/project/linux-riscv/patch/20200917223716.2300238-4-atish.patra@wdc.com/
>
> Can you check if you can still reproduce the issue you were seeing
> with the latest upstream kernel ?
> If yes, please share the steps to reproduce the issue.

No, I don't think I can reproduce it now, thanks!

~Vitaly

> > To fix that, move mmu_enabled toggling to head.S and rename it to
> > _mmu_enabled to avoid possible name clashes since it's not a static
> > variable any more.
> >
> > Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
> > ---
> >  arch/riscv/kernel/head.S |  9 +++++++++
> >  arch/riscv/mm/init.c     | 13 +++++--------
> >  2 files changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 0a4e81b8dc79..33cd57285be3 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -248,6 +248,10 @@ clear_bss_done:
> >         call relocate
> >  #endif /* CONFIG_MMU */
> >
> > +       la a0, _mmu_enabled
> > +       li a1, 1
> > +       sw a1, (a0)
> > +
> >         call setup_trap_vector
> >         /* Restore C environment */
> >         la tp, init_task
> > @@ -370,6 +374,11 @@ ENTRY(reset_regs)
> >  END(reset_regs)
> >  #endif /* CONFIG_RISCV_M_MODE */
> >
> > +.section ".data"
> > +       .global _mmu_enabled
> > +_mmu_enabled:
> > +       .word 0
> > +
> >  __PAGE_ALIGNED_BSS
> >         /* Empty zero page */
> >         .balign PAGE_SIZE
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 787c75f751a5..4038be635e25 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -211,7 +211,7 @@ EXPORT_SYMBOL(pfn_base);
> >  pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> >  pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> >  pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> > -static bool mmu_enabled;
> > +extern bool _mmu_enabled;
> >
> >  #define MAX_EARLY_MAPPING_SIZE SZ_128M
> >
> > @@ -236,7 +236,7 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
> >
> >  static pte_t *__init get_pte_virt(phys_addr_t pa)
> >  {
> > -       if (mmu_enabled) {
> > +       if (_mmu_enabled) {
> >                 clear_fixmap(FIX_PTE);
> >                 return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
> >         } else {
> > @@ -250,7 +250,7 @@ static phys_addr_t __init alloc_pte(uintptr_t va)
> >          * We only create PMD or PGD early mappings so we
> >          * should never reach here with MMU disabled.
> >          */
> > -       BUG_ON(!mmu_enabled);
> > +       BUG_ON(!_mmu_enabled);
> >
> >         return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> >  }
> > @@ -281,7 +281,7 @@ pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
> >
> >  static pmd_t *__init get_pmd_virt(phys_addr_t pa)
> >  {
> > -       if (mmu_enabled) {
> > +       if (_mmu_enabled) {
> >                 clear_fixmap(FIX_PMD);
> >                 return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
> >         } else {
> > @@ -293,7 +293,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
> >  {
> >         uintptr_t pmd_num;
> >
> > -       if (mmu_enabled)
> > +       if (_mmu_enabled)
> >                 return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> >
> >         pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> > @@ -467,9 +467,6 @@ static void __init setup_vm_final(void)
> >         phys_addr_t pa, start, end;
> >         struct memblock_region *reg;
> >
> > -       /* Set mmu_enabled flag */
> > -       mmu_enabled = true;
> > -
> >         /* Setup swapper PGD for fixmap */
> >         create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
> >                            __pa_symbol(fixmap_pgd_next),
> > --
> > 2.20.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>
>
> --
> Regards,
> Atish
diff mbox series

Patch

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 0a4e81b8dc79..33cd57285be3 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -248,6 +248,10 @@  clear_bss_done:
 	call relocate
 #endif /* CONFIG_MMU */
 
+	la a0, _mmu_enabled
+	li a1, 1
+	sw a1, (a0)
+
 	call setup_trap_vector
 	/* Restore C environment */
 	la tp, init_task
@@ -370,6 +374,11 @@  ENTRY(reset_regs)
 END(reset_regs)
 #endif /* CONFIG_RISCV_M_MODE */
 
+.section ".data"
+	.global _mmu_enabled
+_mmu_enabled:
+	.word 0
+
 __PAGE_ALIGNED_BSS
 	/* Empty zero page */
 	.balign PAGE_SIZE
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 787c75f751a5..4038be635e25 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -211,7 +211,7 @@  EXPORT_SYMBOL(pfn_base);
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
-static bool mmu_enabled;
+extern bool _mmu_enabled;
 
 #define MAX_EARLY_MAPPING_SIZE	SZ_128M
 
@@ -236,7 +236,7 @@  void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 
 static pte_t *__init get_pte_virt(phys_addr_t pa)
 {
-	if (mmu_enabled) {
+	if (_mmu_enabled) {
 		clear_fixmap(FIX_PTE);
 		return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
 	} else {
@@ -250,7 +250,7 @@  static phys_addr_t __init alloc_pte(uintptr_t va)
 	 * We only create PMD or PGD early mappings so we
 	 * should never reach here with MMU disabled.
 	 */
-	BUG_ON(!mmu_enabled);
+	BUG_ON(!_mmu_enabled);
 
 	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 }
@@ -281,7 +281,7 @@  pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
 
 static pmd_t *__init get_pmd_virt(phys_addr_t pa)
 {
-	if (mmu_enabled) {
+	if (_mmu_enabled) {
 		clear_fixmap(FIX_PMD);
 		return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
 	} else {
@@ -293,7 +293,7 @@  static phys_addr_t __init alloc_pmd(uintptr_t va)
 {
 	uintptr_t pmd_num;
 
-	if (mmu_enabled)
+	if (_mmu_enabled)
 		return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
 
 	pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
@@ -467,9 +467,6 @@  static void __init setup_vm_final(void)
 	phys_addr_t pa, start, end;
 	struct memblock_region *reg;
 
-	/* Set mmu_enabled flag */
-	mmu_enabled = true;
-
 	/* Setup swapper PGD for fixmap */
 	create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
 			   __pa_symbol(fixmap_pgd_next),