linux-kernel - Re: [RFC PATCH v2 06/32] x86/pci: Use memremap when walking setup data

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Date:   Fri, 3 Mar 2017 14:42:09 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linux-pci@...r.kernel.org, linus.walleij@...aro.org,
        gary.hook@....com, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com, cl@...ux.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
        sfr@...b.auug.org.au, andriy.shevchenko@...ux.intel.com,
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        joro@...tes.org, x86@...nel.org, peterz@...radead.org,
        piotr.luc@...el.com, mingo@...hat.com, msalter@...hat.com,
        ross.zwisler@...ux.intel.com, bp@...e.de, dyoung@...hat.com,
        thomas.lendacky@....com, jroedel@...e.de, keescook@...omium.org,
        arnd@...db.de, toshi.kani@....com, mathieu.desnoyers@...icios.com,
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        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v2 06/32] x86/pci: Use memremap when walking setup
 data

On Thu, Mar 02, 2017 at 10:13:10AM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> The use of ioremap will force the setup data to be mapped decrypted even
> though setup data is encrypted.  Switch to using memremap which will be
> able to perform the proper mapping.

How should callers decide whether to use ioremap() or memremap()?

memremap() existed before SME and SEV, and this code is used even if
SME and SEV aren't supported, so the rationale for this change should
not need the decryption argument.

> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/pci/common.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> index a4fdfa7..0b06670 100644
> --- a/arch/x86/pci/common.c
> +++ b/arch/x86/pci/common.c
> @@ -691,7 +691,7 @@ int pcibios_add_device(struct pci_dev *dev)
>  
>  	pa_data = boot_params.hdr.setup_data;
>  	while (pa_data) {
> -		data = ioremap(pa_data, sizeof(*rom));
> +		data = memremap(pa_data, sizeof(*rom), MEMREMAP_WB);

I can't quite connect the dots here.  ioremap() on x86 would do
ioremap_nocache().  memremap(MEMREMAP_WB) would do arch_memremap_wb(),
which is ioremap_cache().  Is making a cacheable mapping the important
difference?

>  		if (!data)
>  			return -ENOMEM;
>  
> @@ -710,7 +710,7 @@ int pcibios_add_device(struct pci_dev *dev)
>  			}
>  		}
>  		pa_data = data->next;
> -		iounmap(data);
> +		memunmap(data);
>  	}
>  	set_dma_domain_ops(dev);
>  	set_dev_domain_options(dev);
>