linux-kernel - Re: [PATCH v9 1/2] efi: Introduce efi_early_memdesc

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Date:   Wed, 16 Aug 2017 21:18:41 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org, tglx@...utronix.de, hpa@...or.com,
        izumi.taku@...fujitsu.com, fanc.fnst@...fujitsu.com,
        thgarnie@...gle.com, n-horiguchi@...jp.nec.com,
        ard.biesheuvel@...aro.org, linux-efi@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v9 1/2] efi: Introduce efi_early_memdesc_ptr to get
 pointer to memmap descriptor

On 08/16/17 at 12:37pm, Matt Fleming wrote:
> On Mon, 14 Aug, at 10:54:23PM, Baoquan He wrote:
> > The existing map iteration helper for_each_efi_memory_desc_in_map can
> > only be used after OS initializes EFI to fill data of struct efi_memory_map.
> 
> Should this say "EFI subsystem"? The firmware doesn't care about the
> kernel's internal data structures.

Sounds reasonable. Let me update and maybe repost to this thread
directly. Thanks!

> 
> > Before that we also need iterate map descriptors which are stored in several
> > intermediate structures, like struct efi_boot_memmap for arch independent
> > usage and struct efi_info for x86 arch only.
> > 
> > Introduce efi_early_memdesc_ptr to get pointer to a map descriptor, and
> > replace several places of open code with it.
> > 
> > Suggested-by: Ingo Molnar <mingo@...nel.org>
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  arch/x86/boot/compressed/eboot.c               |  2 +-
> >  drivers/firmware/efi/libstub/efi-stub-helper.c |  4 ++--
> >  include/linux/efi.h                            | 21 +++++++++++++++++++++
> >  3 files changed, 24 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> > index c3e869eaef0c..e007887a33b0 100644
> > --- a/arch/x86/boot/compressed/eboot.c
> > +++ b/arch/x86/boot/compressed/eboot.c
> > @@ -767,7 +767,7 @@ static efi_status_t setup_e820(struct boot_params *params,
> >  		m |= (u64)efi->efi_memmap_hi << 32;
> >  #endif
> >  
> > -		d = (efi_memory_desc_t *)(m + (i * efi->efi_memdesc_size));
> > +		d = efi_early_memdesc_ptr(m, efi->efi_memdesc_size, i);
> >  		switch (d->type) {
> >  		case EFI_RESERVED_TYPE:
> >  		case EFI_RUNTIME_SERVICES_CODE:
> > diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> > index b0184360efc6..50a9cab5a834 100644
> > --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> > +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> > @@ -205,7 +205,7 @@ efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
> >  		unsigned long m = (unsigned long)map;
> >  		u64 start, end;
> >  
> > -		desc = (efi_memory_desc_t *)(m + (i * desc_size));
> > +		desc = efi_early_memdesc_ptr(m, desc_size, i);
> >  		if (desc->type != EFI_CONVENTIONAL_MEMORY)
> >  			continue;
> >  
> > @@ -298,7 +298,7 @@ efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
> >  		unsigned long m = (unsigned long)map;
> >  		u64 start, end;
> >  
> > -		desc = (efi_memory_desc_t *)(m + (i * desc_size));
> > +		desc = efi_early_memdesc_ptr(m, desc_size, i);
> >  
> >  		if (desc->type != EFI_CONVENTIONAL_MEMORY)
> >  			continue;
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index 8269bcb8ccf7..9783d9e4a4b2 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -1020,6 +1020,27 @@ extern int efi_memattr_init(void);
> >  extern int efi_memattr_apply_permissions(struct mm_struct *mm,
> >  					 efi_memattr_perm_setter fn);
> >  
> > +/*
> > + * efi_early_memdesc_ptr - get the n-th efi memmap descriptor
> > + * @map: the start of efi memmap
> > + * @desc_size: the size of space for each efi memmap descriptor
> > + * @n: the index of efi memmap descriptor
> > + *
> > + * EFI boot service provides function GetMemoryMap() to get a copy of the
> > + * current memory map which is an array of memory descriptors, each of
> > + * which describes a contiguous block of memory. And also get the size of
> > + * map, and the size of each descriptor, etc. Note that per section 6.2 of
> > + * UEFI Spec 2.6 Errata A, the returned size of each descriptor might not
> > + * be equal to sizeof(efi_memory_memdesc_t) since efi_memory_memdesc_t may
> > + * be extended in the future in response to hardware innovation. Thus OS
> > + * MUST use the returned size of descriptor to find the start of each
> > + * efi_memory_memdesc_t in the memory map array. This should only be used
> > + * during bootup since for_each_efi_memory_desc_xxx is suggested after OS
> > + * initializes EFI to fill data of struct efi_memory_map.
> > + */
> 
> Again, please use "EFI subsystem" here.

Sure, will do.
> 
> > +#define efi_early_memdesc_ptr(map, desc_size, n)			\
> > +	(efi_memory_desc_t *)((void *)(map) + ((n) * (desc_size)))
> > +
> >  /* Iterate through an efi_memory_map */
> >  #define for_each_efi_memory_desc_in_map(m, md)				   \
> >  	for ((md) = (m)->map;						   \
> 
> Otherwise, this looks OK to me.

Thanks for reviewing!