linux-kernel - Re: [RESEND PATCH V3 2/2] riscv: add RISC-V Svpbmt extension supports

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Message-ID: <YXZU/3/YmRGFrOXK@infradead.org>
Date:   Sun, 24 Oct 2021 23:55:59 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     wefu@...hat.com
Cc:     anup.patel@....com, atish.patra@....com, palmerdabbelt@...gle.com,
        guoren@...nel.org, christoph.muellner@...ll.eu,
        philipp.tomsich@...ll.eu, hch@....de, liush@...winnertech.com,
        lazyparser@...il.com, drew@...gleboard.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        taiten.peng@...onical.com, aniket.ponkshe@...onical.com,
        heinrich.schuchardt@...onical.com, gordan.markus@...onical.com,
        guoren@...ux.alibaba.com, arnd@...db.de, wens@...e.org,
        maxime@...no.tech, dlustig@...dia.com, gfavor@...tanamicro.com,
        andrea.mondelli@...wei.com, behrensj@....edu, xinhaoqu@...wei.com,
        huffman@...ence.com, mick@....forth.gr,
        allen.baum@...erantotech.com, jscheid@...tanamicro.com,
        rtrauben@...il.com
Subject: Re: [RESEND PATCH V3 2/2] riscv: add RISC-V Svpbmt extension supports

On Mon, Oct 25, 2021 at 12:06:07PM +0800, wefu@...hat.com wrote:
>  static inline pmd_t *pud_pgtable(pud_t pud)
>  {
> -	return (pmd_t *)pfn_to_virt(pud_val(pud) >> _PAGE_PFN_SHIFT);
> +	return (pmd_t *)pfn_to_virt((pud_val(pud) & _PAGE_CHG_MASK)
> +						>> _PAGE_PFN_SHIFT);
>  }
>  
>  static inline struct page *pud_page(pud_t pud)
>  {
> -	return pfn_to_page(pud_val(pud) >> _PAGE_PFN_SHIFT);
> +	return pfn_to_page((pud_val(pud) & _PAGE_CHG_MASK)
> +						>> _PAGE_PFN_SHIFT);

>  static inline unsigned long _pmd_pfn(pmd_t pmd)
>  {
> -	return pmd_val(pmd) >> _PAGE_PFN_SHIFT;
> +	return (pmd_val(pmd) & _PAGE_CHG_MASK) >> _PAGE_PFN_SHIFT;
>  }

The "(pud_val(pud) & _PAGE_CHG_MASK) >> _PAGE_PFN_SHIFT" expression begs
for readable and well-documented helper.

> +#define _SVPBMT_PMA		((unsigned long)0x0 << 61)
> +#define _SVPBMT_NC		((unsigned long)0x1 << 61)
> +#define _SVPBMT_IO		((unsigned long)0x2 << 61)

0UL << 61
1UL << 61
...

> +#define _SVPBMT_MASK		(_SVPBMT_PMA | _SVPBMT_NC | _SVPBMT_IO)
> +
> +extern struct __riscv_svpbmt_struct {
> +	unsigned long mask;
> +	unsigned long mt_pma;
> +	unsigned long mt_nc;
> +	unsigned long mt_io;
> +} __riscv_svpbmt;
> +
> +#define _PAGE_MT_MASK		__riscv_svpbmt.mask
> +#define _PAGE_MT_PMA		__riscv_svpbmt.mt_pma
> +#define _PAGE_MT_NC		__riscv_svpbmt.mt_nc
> +#define _PAGE_MT_IO		__riscv_svpbmt.mt_io

Using a struct over individual variables seems a little odd here.

Also why not use the standard names for these _PAGE bits used by
most other architectures?

> -	return (unsigned long)pfn_to_virt(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
> +	return (unsigned long)pfn_to_virt((pmd_val(pmd) & _PAGE_CHG_MASK) >> _PAGE_PFN_SHIFT);

Overly long line, could use a helper.  Btw, what is the point in having
this _PAGE_PFN_SHIFT macro to start with?