On 1/9/23 23:13, Frank van der Linden wrote:
> The page table debug tests need a physical address to validate
> low-level page table manipulation with. The memory at this address
> is not actually touched, it just encoded in the page table entries
> at various levels during the tests only.
>
> Since the memory is not used, the code just picks the physical
> address of the start_kernel symbol. This value is then truncated
> to get a properly aligned address that is to be used for various
> tests. Because of the truncation, the address might not actually
> exist, or might not describe a complete huge page. That's not a
> problem for most tests, but the arch-specific code may check
> for attribute validity and consistency. The x86 version of
> {pud,pmd}_set_huge actually validates the MTRRs for the PMD/PUD
> range. This may fail with an address derived from start_kernel,
> depending on where the kernel was loaded and what the physical
> memory layout of the system is. This then leads to false negatives
> for the {pud,pmd}_set_huge tests.
>
> Avoid this by finding a properly aligned memory range that exists
> and is usable. If such a range is not found, skip the tests that
> needed it.
>
> Fixes: 399145f9eb6c ("mm/debug: add tests validating architecture page table helpers")
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Signed-off-by: Frank van der Linden <fvdl@xxxxxxxxxx>
> ---
> mm/debug_vm_pgtable.c | 103 ++++++++++++++++++++++++++++++++++--------
> 1 file changed, 84 insertions(+), 19 deletions(-)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index c631ade3f1d2..503358332c92 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -15,6 +15,7 @@
> #include <linux/hugetlb.h>
> #include <linux/kernel.h>
> #include <linux/kconfig.h>
> +#include <linux/memblock.h>
> #include <linux/mm.h>
> #include <linux/mman.h>
> #include <linux/mm_types.h>
> @@ -80,6 +81,7 @@ struct pgtable_debug_args {
> unsigned long pmd_pfn;
> unsigned long pte_pfn;
>
> + unsigned long fixed_alignment;
> unsigned long fixed_pgd_pfn;
> unsigned long fixed_p4d_pfn;
> unsigned long fixed_pud_pfn;
> @@ -430,7 +432,8 @@ static void __init pmd_huge_tests(struct pgtable_debug_args *args)
> {
> pmd_t pmd;
>
> - if (!arch_vmap_pmd_supported(args->page_prot))
> + if (!arch_vmap_pmd_supported(args->page_prot) ||
> + args->fixed_alignment < PMD_SIZE)
> return;
>
> pr_debug("Validating PMD huge\n");
> @@ -449,7 +452,8 @@ static void __init pud_huge_tests(struct pgtable_debug_args *args)
> {
> pud_t pud;
>
> - if (!arch_vmap_pud_supported(args->page_prot))
> + if (!arch_vmap_pud_supported(args->page_prot) ||
> + args->fixed_alignment < PUD_SIZE)
> return;
>
> pr_debug("Validating PUD huge\n");
> @@ -1077,10 +1081,86 @@ debug_vm_pgtable_alloc_huge_page(struct pgtable_debug_args *args, int order)
> return page;
> }
>
> +/*
> + * Check if a physical memory range described by <pstart, pend> contains
> + * an area that is of size psize, and aligned to psize.
> + *
> + * Don't use address 0, an all-zeroes physical address might mask bugs, and
> + * it's not used on x86.
> + */
> +static void __init phys_align_check(phys_addr_t pstart,
> + phys_addr_t pend, unsigned long psize, phys_addr_t *physp,
> + unsigned long *alignp)
Small nit. The arguments here need to be aligned properly.
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 503358332c92..7bdc6f41a6a6 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -1088,9 +1088,9 @@ debug_vm_pgtable_alloc_huge_page(struct pgtable_debug_args *args, int order)
* Don't use address 0, an all-zeroes physical address might mask bugs, and
* it's not used on x86.
*/
-static void __init phys_align_check(phys_addr_t pstart,
- phys_addr_t pend, unsigned long psize, phys_addr_t *physp,
- unsigned long *alignp)
+static void __init phys_align_check(phys_addr_t pstart, phys_addr_t pend,
+ unsigned long psize, phys_addr_t *physp,
+ unsigned long *alignp)
{
phys_addr_t aligned_start, aligned_end;
> +{
> + phys_addr_t aligned_start, aligned_end;
> +
> + if (pstart == 0)
> + pstart = PAGE_SIZE;
> +
> + aligned_start = ALIGN(pstart, psize);
> + aligned_end = aligned_start + psize;
> +
> + if (aligned_end > aligned_start && aligned_end <= pend) {
> + *alignp = psize;
> + *physp = aligned_start;
> + }
> +}
> +
> +static void __init init_fixed_pfns(struct pgtable_debug_args *args)
> +{
> + u64 idx;
> + phys_addr_t phys, pstart, pend;
> +
> + /*
> + * Initialize the fixed pfns. To do this, try to find a
> + * valid physical range, preferably aligned to PUD_SIZE,
> + * but settling for aligned to PMD_SIZE as a fallback. If
> + * neither of those is found, use the physical address of
> + * the start_kernel symbol.
> + *
> + * The memory doesn't need to be allocated, it just needs to exist
> + * as usable memory. It won't be touched.
> + *
> + * The alignment is recorded, and can be checked to see if we
> + * can run the tests that require an actual valid physical
> + * address range on some architectures ({pmd,pud}_huge_test
> + * on x86).
> + */
> +
> + phys = __pa_symbol(&start_kernel);
> + args->fixed_alignment = PAGE_SIZE;
> +
> + for_each_mem_range(idx, &pstart, &pend) {
> + /* First check for a PUD-aligned area */
> + phys_align_check(pstart, pend, PUD_SIZE, &phys,
> + &args->fixed_alignment);
Please align the second line properly as above or better just move it in a
single line exceeding 80.
> +
> + /* If a PUD-aligned area is found, we're done */
> + if (args->fixed_alignment >= PUD_SIZE)
> + break;
This check should be "args->fixed_alignment == PUD_SIZE" because the previous
call into phys_align_check() was with PUD_SIZE size and alignment request. So
it could not have achieved args->fixed_alignment larger than PUD_SIZE ?
> +
> + /*
> + * If no PMD-aligned area found yet, check for one,
> + * but continue the loop to look for a PUD-aligned area.
> + */
> + if (args->fixed_alignment < PMD_SIZE) {
> + phys_align_check(pstart, pend, PMD_SIZE, &phys,
> + &args->fixed_alignment);
Moving this into previous line will fix the alignment problem and also will
help drop these additional redundant braces here. In case these lines are
decided to be folded back, please also follow the same for the conditional
statements in pmd_huge_tests/pud_huge_tests as mentioned earlier.
> + }
> + }
> +
> + args->fixed_pgd_pfn = __phys_to_pfn(phys & PGDIR_MASK);
> + args->fixed_p4d_pfn = __phys_to_pfn(phys & P4D_MASK);
> + args->fixed_pud_pfn = __phys_to_pfn(phys & PUD_MASK);
> + args->fixed_pmd_pfn = __phys_to_pfn(phys & PMD_MASK);
> + args->fixed_pte_pfn = __phys_to_pfn(phys & PAGE_MASK);
> + WARN_ON(!pfn_valid(args->fixed_pte_pfn));
> +}
> +
> +
> static int __init init_args(struct pgtable_debug_args *args)
> {
> struct page *page = NULL;
> - phys_addr_t phys;
> int ret = 0;
>
> /*
> @@ -1160,22 +1240,7 @@ static int __init init_args(struct pgtable_debug_args *args)
> args->start_ptep = pmd_pgtable(READ_ONCE(*args->pmdp));
> WARN_ON(!args->start_ptep);
>
> - /*
> - * PFN for mapping at PTE level is determined from a standard kernel
> - * text symbol. But pfns for higher page table levels are derived by
> - * masking lower bits of this real pfn. These derived pfns might not
> - * exist on the platform but that does not really matter as pfn_pxx()
> - * helpers will still create appropriate entries for the test. This
> - * helps avoid large memory block allocations to be used for mapping
> - * at higher page table levels in some of the tests.
> - */
> - phys = __pa_symbol(&start_kernel);
> - args->fixed_pgd_pfn = __phys_to_pfn(phys & PGDIR_MASK);
> - args->fixed_p4d_pfn = __phys_to_pfn(phys & P4D_MASK);
> - args->fixed_pud_pfn = __phys_to_pfn(phys & PUD_MASK);
> - args->fixed_pmd_pfn = __phys_to_pfn(phys & PMD_MASK);
> - args->fixed_pte_pfn = __phys_to_pfn(phys & PAGE_MASK);
> - WARN_ON(!pfn_valid(args->fixed_pte_pfn));
> + init_fixed_pfns(args);
>
> /*
> * Allocate (huge) pages because some of the tests need to access
With the suggested changes accommodated
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
