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

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Message-ID: <56f89895-601e-44c9-bda4-5fae6782e27e@amd.com>
Date:   Mon, 9 May 2022 11:06:22 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     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>,
        Brijesh Singh <brijesh.singh@....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 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.

Thanks,
Tom

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