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SubjectRe: [patch 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

* Thomas Gleixner <tglx@linutronix.de> wrote:

> From: Song Liu <songliubraving@fb.com>
>
> pti_clone_pmds() assumes that the supplied address is either:
>
> - properly PUD/PMD aligned
> or
> - the address is actually mapped which means that independent
> of the mapping level (PUD/PMD/PTE) the next higher mapping
> exist.

s/independent
/independently

s/exist
/exists

> If that's not the case the unaligned address can be incremented by PUD or
> PMD size wrongly. All callers supply mapped and/or aligned addresses, but
> for robustness sake, it's better to handle that case proper and to emit a
> warning.

s/wrongly
/incorrectly

s/robustness sake
/robustness's sake

s/proper
/properly

With that:

> pud = pud_offset(p4d, addr);
> if (pud_none(*pud)) {
> - addr += PUD_SIZE;
> + WARN_ON_ONCE(addr & PUD_MASK);
> + addr = round_up(addr + 1, PUD_SIZE);
> continue;
> }
>
> pmd = pmd_offset(pud, addr);
> if (pmd_none(*pmd)) {
> - addr += PMD_SIZE;
> + WARN_ON_ONCE(addr & PMD_MASK);
> + addr = round_up(addr + 1, PMD_SIZE);

So given that PUD_MASK and PMD_MASK are masking out the *offset*:

arch/x86/include/asm/pgtable_64_types.h:#define PMD_MASK (~(PMD_SIZE - 1))

Didn't we want something like:

WARN_ON_ONCE(addr & ~PUD_MASK);

WARN_ON_ONCE(addr & ~PMD_MASK);

to warn about an unaligned 'addr', or am I misreading the intent here?

Thanks,

Ingo

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