linux-kernel - Re: [PATCH 2 of 7] x86/pvops: add a paravirt_ident functions to allow special patching

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Message-Id: <200901291835.49251.rusty@rustcorp.com.au>
Date:	Thu, 29 Jan 2009 18:35:48 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Xen-devel" <xen-devel@...ts.xensource.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Zachary Amsden <zach@...are.com>,
	Ravikiran Thirumalai <kiran@...lemp.com>
Subject: Re: [PATCH 2 of 7] x86/pvops: add a paravirt_ident functions to allow special patching

On Thursday 29 January 2009 09:05:02 Jeremy Fitzhardinge wrote:
>  void _paravirt_nop(void);
> +u32 _paravirt_ident_32(u32);
> +u64 _paravirt_ident_64(u64);
> +
>  #define paravirt_nop	((void *)_paravirt_nop)

So, we used a void * cast for the paravirt_nop case, but you decided to use explicit types for the ident cases?

>  	if (opfunc == NULL)
>  		/* If there's no function, patch it with a ud2a (BUG) */
>  		ret = paravirt_patch_insns(insnbuf, len, ud2a, ud2a+sizeof(ud2a));
> -	else if (opfunc == paravirt_nop)
> +	else if (opfunc == _paravirt_nop)
>  		/* If the operation is a nop, then nop the callsite */
>  		ret = paravirt_patch_nop();

Gratuitous change?

> +typedef pte_t make_pte_t(pteval_t);
> +typedef pmd_t make_pmd_t(pmdval_t);
> +typedef pud_t make_pud_t(pudval_t);
> +typedef pgd_t make_pgd_t(pgdval_t);
> +
> +typedef pteval_t pte_val_t(pte_t);
> +typedef pmdval_t pmd_val_t(pmd_t);
> +typedef pudval_t pud_val_t(pud_t);
> +typedef pgdval_t pgd_val_t(pgd_t);
> +
> +
> +#if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE)
> +/* 32-bit pagetable entries */
> +#define paravirt_native_make_pte	(make_pte_t *)_paravirt_ident_32
> +#define paravirt_native_pte_val		(pte_val_t *)_paravirt_ident_32
> +
> +#define paravirt_native_make_pmd	(make_pmd_t *)_paravirt_ident_32
> +#define paravirt_native_pmd_val		(pmd_val_t *)_paravirt_ident_32
> +
> +#define paravirt_native_make_pud	(make_pud_t *)_paravirt_ident_32
> +#define paravirt_native_pud_val		(pud_val_t *)_paravirt_ident_32
> +
> +#define paravirt_native_make_pgd	(make_pgd_t *)_paravirt_ident_32
> +#define paravirt_native_pgd_val		(pgd_val_t *)_paravirt_ident_32
> +#else
> +/* 64-bit pagetable entries */
> +#define paravirt_native_make_pte	(make_pte_t *)_paravirt_ident_64
> +#define paravirt_native_pte_val		(pte_val_t *)_paravirt_ident_64
> +
> +#define paravirt_native_make_pmd	(make_pmd_t *)_paravirt_ident_64
> +#define paravirt_native_pmd_val		(pmd_val_t *)_paravirt_ident_64
> +
> +#define paravirt_native_make_pud	(make_pud_t *)_paravirt_ident_64
> +#define paravirt_native_pud_val		(pud_val_t *)_paravirt_ident_64
> +
> +#define paravirt_native_make_pgd	(make_pgd_t *)_paravirt_ident_64
> +#define paravirt_native_pgd_val		(pgd_val_t *)_paravirt_ident_64
> +#endif

I think I prefer:

/* make_pte etc and pgd_val etc are identity functions. */
#define paravirt_native_page_op \
	(sizeof(pte_t) == sizeof(u64) ? paravirt_ident_64 : paravirt_ident_32)

Then use that everywhere rather than these defines?

But it's a minor point; the code seems perfectly sound.

Acked-by: Rusty Russell <rusty@...tcorp.com.au>

Thanks!
Rusty.
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