linux-kernel - Re: [PATCH v2 2/4] ioremap: Implement TLB

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Date:   Thu, 15 Mar 2018 13:13:16 +0000
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 v2 2/4] ioremap: Implement TLB_INV before huge mapping

Hi,

As a general note, pleas wrap commit text to 72 characters.

On Thu, Mar 15, 2018 at 06:15:04PM +0530, Chintan Pandya wrote:
> Huge mapping changes PMD/PUD which could have
> valid previous entries. This requires proper
> TLB maintanance on some architectures, like
> ARM64.

Just to check, I take it that you mean we could have a valid table
entry, but all the entries in that next level table must be invalid,
right?

> 
> Implent BBM (break-before-make) safe TLB
> invalidation.
> 
> Here, I've used flush_tlb_pgtable() instead
> of flush_kernel_range() because invalidating
> intermediate page_table entries could have
> been optimized for specific arch. That's the
> case with ARM64 at least.

... because if there are valid entries in the next level table,
__flush_tlb_pgtable() is not sufficient to ensure all of these are
removed from the TLB.

Assuming that all entries in the next level table are invalid, this
looks ok to me.

Thanks,
Mark.

> Signed-off-by: Chintan Pandya <cpandya@...eaurora.org>
> ---
>  lib/ioremap.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/ioremap.c b/lib/ioremap.c
> index 54e5bba..55f8648 100644
> --- a/lib/ioremap.c
> +++ b/lib/ioremap.c
> @@ -13,6 +13,7 @@
>  #include <linux/export.h>
>  #include <asm/cacheflush.h>
>  #include <asm/pgtable.h>
> +#include <asm-generic/tlb.h>
>  
>  #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
>  static int __read_mostly ioremap_p4d_capable;
> @@ -80,6 +81,7 @@ static inline int ioremap_pmd_range(pud_t *pud, unsigned long addr,
>  		unsigned long end, phys_addr_t phys_addr, pgprot_t prot)
>  {
>  	pmd_t *pmd;
> +	pmd_t old_pmd;
>  	unsigned long next;
>  
>  	phys_addr -= addr;
> @@ -91,10 +93,15 @@ static inline int ioremap_pmd_range(pud_t *pud, unsigned long addr,
>  
>  		if (ioremap_pmd_enabled() &&
>  		    ((next - addr) == PMD_SIZE) &&
> -		    IS_ALIGNED(phys_addr + addr, PMD_SIZE) &&
> -		    pmd_free_pte_page(pmd)) {
> -			if (pmd_set_huge(pmd, phys_addr + addr, prot))
> +		    IS_ALIGNED(phys_addr + addr, PMD_SIZE)) {
> +			old_pmd = *pmd;
> +			pmd_clear(pmd);
> +			flush_tlb_pgtable(&init_mm, addr);
> +			if (pmd_set_huge(pmd, phys_addr + addr, prot)) {
> +				pmd_free_pte_page(&old_pmd);
>  				continue;
> +			} else
> +				set_pmd(pmd, old_pmd);
>  		}
>  
>  		if (ioremap_pte_range(pmd, addr, next, phys_addr + addr, prot))
> @@ -107,6 +114,7 @@ static inline int ioremap_pud_range(p4d_t *p4d, unsigned long addr,
>  		unsigned long end, phys_addr_t phys_addr, pgprot_t prot)
>  {
>  	pud_t *pud;
> +	pud_t old_pud;
>  	unsigned long next;
>  
>  	phys_addr -= addr;
> @@ -118,10 +126,15 @@ static inline int ioremap_pud_range(p4d_t *p4d, unsigned long addr,
>  
>  		if (ioremap_pud_enabled() &&
>  		    ((next - addr) == PUD_SIZE) &&
> -		    IS_ALIGNED(phys_addr + addr, PUD_SIZE) &&
> -		    pud_free_pmd_page(pud)) {
> -			if (pud_set_huge(pud, phys_addr + addr, prot))
> +		    IS_ALIGNED(phys_addr + addr, PUD_SIZE)) {
> +			old_pud = *pud;
> +			pud_clear(pud);
> +			flush_tlb_pgtable(&init_mm, addr);
> +			if (pud_set_huge(pud, phys_addr + addr, prot)) {
> +				pud_free_pmd_page(&old_pud);
>  				continue;
> +			} else
> +				set_pud(pud, old_pud);
>  		}
>  
>  		if (ioremap_pmd_range(pud, addr, next, phys_addr + addr, prot))
> -- 
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation
> Center, Inc., is a member of Code Aurora Forum, a Linux Foundation
> Collaborative Project
>