linux-kernel - Re: [PATCH v4 2/3] arm64: Implement page table free interfaces

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Message-ID: <20180326095541.izogc4iak6d7nerm@lakrids.cambridge.arm.com>
Date:   Mon, 26 Mar 2018 10:55:41 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Chintan Pandya <cpandya@...eaurora.org>
Cc:     catalin.marinas@....com, will.deacon@....com, arnd@...db.de,
        ard.biesheuvel@...aro.org, marc.zyngier@....com,
        james.morse@....com, kristina.martsenko@....com,
        takahiro.akashi@...aro.org, gregkh@...uxfoundation.org,
        tglx@...utronix.de, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        akpm@...ux-foundation.org, toshi.kani@....com
Subject: Re: [PATCH v4 2/3] arm64: Implement page table free interfaces

On Tue, Mar 20, 2018 at 05:15:13PM +0530, Chintan Pandya wrote:
> +static int __pmd_free_pte_page(pmd_t *pmd, unsigned long addr, bool tlb_inv)
> +{
> +	pmd_t *table;
> +
> +	if (pmd_val(*pmd)) {
> +		table = __va(pmd_val(*pmd));
> +		pmd_clear(pmd);
> +		/*
> +		 * FIXME: __flush_tlb_pgtable(&init_mm, addr) is
> +		 *        ideal candidate here, which exactly
> +		 *        flushes intermediate pgtables. But,
> +		 *        this is broken (evident from tests).
> +		 *        So, use safe TLB op unless that is fixed.
> +		 */
> +		if (tlb_inv)
> +			flush_tlb_kernel_range(addr, addr + PMD_SIZE);

I don't think that __flush_tlb_pgtable() is broken. It's only valid to
call it for user page tables, since it doesn't affect all ASIDs.

We can add a simlar helper for kernel mappings, which affects all ASIDs,
e.g.

static inline void __flush_tlb_kernel_pgtable(unsigned long addr)
{
	addr >>= 12;
	__tlbi(vaae1is, addr);
	dsb(ish);
}

Thanks,
Mark.