linux-kernel - Re: [PATCH] x86/mm/cpa: set PAGE_KERNEL in __set_pages

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Date:   Tue, 10 May 2022 20:57:16 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm/cpa: set PAGE_KERNEL in __set_pages_p()

On Mon, May 09, 2022 at 11:06:22AM -0500, Tom Lendacky wrote:
> On 5/6/22 00:19, Hyeonggon Yoo wrote:
> > __set_pages_np() not only clears _PAGE_PRESENT and _PAGE_RW, but also
> > clears _PAGE_GLOBAL to avoid confusing _PAGE_GLOBAL as _PAGE_PROTNONE
> > when the PTE is not present.
> > 
> > Common usage for __set_pages_p() is to call it after __set_pages_np().
> > Therefore calling __set_pages_p() after __set_pages_np() clears
> > _PAGE_GLOBAL, making it unable to globally shared in TLB.
> > 
> > As they are called by set_direct_map_{invalid,default}_noflush(),
> > pages in direct map cannot be globally shared in TLB after being used by
> > vmalloc, secretmem, and hibernation.
> > 
> > So set PAGE_KERNEL isntead of __pgprot(_PAGE_PRESENT | _PAGE_RW) in
> > __set_pages_p().
> > 
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> > ---
> >   arch/x86/mm/pat/set_memory.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index abf5ed76e4b7..fcb6147c4cd4 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -2177,7 +2177,7 @@ static int __set_pages_p(struct page *page, int numpages)
> >   	struct cpa_data cpa = { .vaddr = &tempaddr,
> >   				.pgd = NULL,
> >   				.numpages = numpages,
> > -				.mask_set = __pgprot(_PAGE_PRESENT | _PAGE_RW),
> > +				.mask_set = PAGE_KERNEL,
> 
> With SME/SEV, this will also (unintentionally) set the encryption bit, so I
> don't think this is correct.
>

Thank you for catching this.
It seems PAGE_KERNEL was too much for  __set_pages_p().

I think __pgprot_mask(_PAGE_KERNEL | _PAGE_RW | _PAGE_GLOBAL) would be correct.
Thoughts?

> Thanks,
> Tom
> 
> >   				.mask_clr = __pgprot(0),
> >   				.flags = 0};

-- 
Thanks,
Hyeonggon