linux-kernel - Re: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi

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Date:   Mon, 29 Oct 2018 18:13:35 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions
 from efi_pgd

Sai,

On Fri, 26 Oct 2018, Sai Praneeth Prakhya wrote:
>  
> +int kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,
> +			      unsigned long numpages)
> +{
> +	int retval;
> +
> +	/*
> +	 * The typical sequence for unmapping is to find a pte through
> +	 * lookup_address_in_pgd() (ideally, it should never return NULL because
> +	 * the address is already mapped) and change it's protections.
> +	 * As pfn is the *target* of a mapping, it's not useful while unmapping.
> +	 */
> +	struct cpa_data cpa = {
> +		.vaddr		= &address,
> +		.pgd		= pgd,
> +		.numpages	= numpages,
> +		.mask_set	= __pgprot(0),
> +		.mask_clr	= __pgprot(_PAGE_PRESENT | _PAGE_RW),
> +		.flags		= 0,
> +	};
> +
> +	retval = __change_page_attr_set_clr(&cpa, 0);
> +	__flush_tlb_all();

So this looks like you copied it from kernel_map_pages_in_pgd() which has
been discussed before to be not sufficient, but it can't be changed right
now due to locking issues.

For this particular use case, this should not be an issue at all, so please
use the proper cpa_flush_*() variant.

> +
> +	return retval;
> +}
> +
>  /*
>   * The testcases use internal knowledge of the implementation that shouldn't
>   * be exposed to the rest of the kernel. Include these directly here.
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index 669babcaf245..fb1c44b11235 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c

While you are at it, can you please split the EFI part out into a separate
patch?

Thanks,

	tglx