linux-kernel - Re: [Xen-devel] [PATCH 2/2] x86/xen/efi: Init only efi struct members used by Xen

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Date:   Wed, 21 Jun 2017 11:29:19 +0200
From:   Daniel Kiper <daniel.kiper@...cle.com>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, stable@...r.kernel.org,
        xen-devel@...ts.xenproject.org, jgross@...e.com,
        ard.biesheuvel@...aro.org, matt@...eblueprint.co.uk,
        mingo@...hat.com, hpa@...or.com, boris.ostrovsky@...cle.com,
        tglx@...utronix.de
Subject: Re: [Xen-devel] [PATCH 2/2] x86/xen/efi: Init only efi struct
 members used by Xen

On Wed, Jun 21, 2017 at 09:10:51AM +0100, Andrew Cooper wrote:
> On 20/06/2017 21:14, Daniel Kiper wrote:
> > Current approach, wholesale efi struct initialization from efi_xen, is not
> > good. Usually if new member is defined then it is properly initialized in
> > drivers/firmware/efi/efi.c but not in arch/x86/xen/efi.c. As I saw it happened
> > a few times until now. So, let's initialize only efi struct members used by
> > Xen to avoid such issues in the future.
> >
> > Signed-off-by: Daniel Kiper <daniel.kiper@...cle.com>
> > ---
> >  arch/x86/xen/efi.c |   45 ++++++++++++---------------------------------
> >  1 file changed, 12 insertions(+), 33 deletions(-)
> >
> > diff --git a/arch/x86/xen/efi.c b/arch/x86/xen/efi.c
> > index 30bb2e8..01b9faf 100644
> > --- a/arch/x86/xen/efi.c
> > +++ b/arch/x86/xen/efi.c
> > @@ -54,38 +54,6 @@
> >  	.tables		= EFI_INVALID_TABLE_ADDR  /* Initialized later. */
> >  };
> >
> > -static const struct efi efi_xen __initconst = {
> > -	.systab                   = NULL, /* Initialized later. */
> > -	.runtime_version	  = 0,    /* Initialized later. */
> > -	.mps                      = EFI_INVALID_TABLE_ADDR,
> > -	.acpi                     = EFI_INVALID_TABLE_ADDR,
> > -	.acpi20                   = EFI_INVALID_TABLE_ADDR,
> > -	.smbios                   = EFI_INVALID_TABLE_ADDR,
> > -	.smbios3                  = EFI_INVALID_TABLE_ADDR,
> > -	.sal_systab               = EFI_INVALID_TABLE_ADDR,
> > -	.boot_info                = EFI_INVALID_TABLE_ADDR,
> > -	.hcdp                     = EFI_INVALID_TABLE_ADDR,
> > -	.uga                      = EFI_INVALID_TABLE_ADDR,
> > -	.uv_systab                = EFI_INVALID_TABLE_ADDR,
> > -	.fw_vendor                = EFI_INVALID_TABLE_ADDR,
> > -	.runtime                  = EFI_INVALID_TABLE_ADDR,
> > -	.config_table             = EFI_INVALID_TABLE_ADDR,
> > -	.get_time                 = xen_efi_get_time,
> > -	.set_time                 = xen_efi_set_time,
> > -	.get_wakeup_time          = xen_efi_get_wakeup_time,
> > -	.set_wakeup_time          = xen_efi_set_wakeup_time,
> > -	.get_variable             = xen_efi_get_variable,
> > -	.get_next_variable        = xen_efi_get_next_variable,
> > -	.set_variable             = xen_efi_set_variable,
> > -	.query_variable_info      = xen_efi_query_variable_info,
> > -	.update_capsule           = xen_efi_update_capsule,
> > -	.query_capsule_caps       = xen_efi_query_capsule_caps,
> > -	.get_next_high_mono_count = xen_efi_get_next_high_mono_count,
> > -	.reset_system             = xen_efi_reset_system,
> > -	.set_virtual_address_map  = NULL, /* Not used under Xen. */
> > -	.flags			  = 0     /* Initialized later. */
> > -};
> > -
> >  static efi_system_table_t __init *xen_efi_probe(void)
> >  {
> >  	struct xen_platform_op op = {
> > @@ -102,7 +70,18 @@ static efi_system_table_t __init *xen_efi_probe(void)
> >
> >  	/* Here we know that Xen runs on EFI platform. */
> >
> > -	efi = efi_xen;
> > +	efi.get_time = xen_efi_get_time;
> > +	efi.set_time = xen_efi_set_time;
> > +	efi.get_wakeup_time = xen_efi_get_wakeup_time;
> > +	efi.set_wakeup_time = xen_efi_set_wakeup_time;
> > +	efi.get_variable = xen_efi_get_variable;
> > +	efi.get_next_variable = xen_efi_get_next_variable;
> > +	efi.set_variable = xen_efi_set_variable;
> > +	efi.query_variable_info = xen_efi_query_variable_info;
> > +	efi.update_capsule = xen_efi_update_capsule;
> > +	efi.query_capsule_caps = xen_efi_query_capsule_caps;
> > +	efi.get_next_high_mono_count = xen_efi_get_next_high_mono_count;
> > +	efi.reset_system = xen_efi_reset_system;
>
> This presumably means that the system default values are already present
> in efi at the point that we overwrite some Xen specifics?

More or less.

> If so, surely you need to retain the clobbering of set_virtual_address_map ?

Nope, by default efi.set_virtual_address_map is NULL (please take a look
at efi struct initialization in drivers/firmware/efi/efi.c). And it is
not touched if efi_enabled(EFI_PARAVIRT).

Daniel