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 18:21:41 +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 Mon, 29 Oct 2018, Thomas Gleixner wrote:
> 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.

Managed to confuse myself. The place which cannot be changed is a different
one, but still for your call site __flush_tlb_all() might not be sufficient.

Thanks,

	tglx