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Subject: Re: [PATCH 4/5] x86/mm: Provide helpers for unaccepted memory
To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>
Cc:     Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Varad Gautam <varad.gautam@suse.com>,
        Dario Faggioli <dfaggioli@suse.com>, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20210810062626.1012-1-kirill.shutemov@linux.intel.com>
 <20210810062626.1012-5-kirill.shutemov@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <67ce254c-aacc-43b6-d8d5-168ef9200f9e@intel.com>
Date:   Tue, 10 Aug 2021 11:16:26 -0700
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Precedence: bulk

On 8/9/21 11:26 PM, Kirill A. Shutemov wrote:
> +void accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	if (!boot_params.unaccepted_memory)
> +		return;
> +
> +	spin_lock(&unaccepted_memory_lock);
> +	__accept_memory(start, end);
> +	spin_unlock(&unaccepted_memory_lock);
> +}

Isn't this taken in the:

	del_page_from_free_list()->
	clear_page_offline()->
	accept_memory()

call path?

That's underneath:

	spin_lock_irqsave(&zone->lock, flags);

Which means that accept_memory() can happen from interrupt context.  Is
it always covered by another spin_lock_irqsave() which means that it can
use a plain spin_lock()?

If so, it would be nice to call out that logic.  It *looks* like a
spinlock that we would want to be spin_lock_irqsave().