linux-kernel - Re: [PATCHv13 5/9] efi: Add unaccepted memory support

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Date:   Mon, 5 Jun 2023 17:43:33 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        aarcange@...hat.com, peterx@...hat.com, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv13 5/9] efi: Add unaccepted memory support

On Thu, Jun 01, 2023 at 09:25:39PM +0300, Kirill A. Shutemov wrote:
> +void accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	struct efi_unaccepted_memory *unaccepted;
> +	unsigned long range_start, range_end;
> +	unsigned long flags;
> +	u64 unit_size;
> +
> +	if (efi.unaccepted == EFI_INVALID_TABLE_ADDR)
> +		return;

efi_get_unaccepted_table() already does this test.

> +	unaccepted = efi_get_unaccepted_table();
> +	if (!unaccepted)
> +		return;

So this looks weird: callers can call accept_memory() and that function
can fail. But they can't know whether it failed or not because it
returns void.

> +	unit_size = unaccepted->unit_size;
> +
> +	/*
> +	 * Only care for the part of the range that is represented
> +	 * in the bitmap.
> +	 */
> +	if (start < unaccepted->phys_base)
> +		start = unaccepted->phys_base;

So this silently trims start...

> +	if (end < unaccepted->phys_base)
> +		return;

But fails only when end is outside of range.

I'd warn here at least. And return an error so that the callers know.

> +	/* Translate to offsets from the beginning of the bitmap */
> +	start -= unaccepted->phys_base;
> +	end -= unaccepted->phys_base;
> +
> +	/* Make sure not to overrun the bitmap */
> +	if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
> +		end = unaccepted->size * unit_size * BITS_PER_BYTE;

How is all that trimming not important to the caller?

It would assume that its memory got accepted but not really.

> +	range_start = start / unit_size;
> +
> +	spin_lock_irqsave(&unaccepted_memory_lock, flags);
> +	for_each_set_bitrange_from(range_start, range_end, unaccepted->bitmap,
> +				   DIV_ROUND_UP(end, unit_size)) {
> +		unsigned long phys_start, phys_end;
> +		unsigned long len = range_end - range_start;
> +
> +		phys_start = range_start * unit_size + unaccepted->phys_base;
> +		phys_end = range_end * unit_size + unaccepted->phys_base;
> +
> +		arch_accept_memory(phys_start, phys_end);
> +		bitmap_clear(unaccepted->bitmap, range_start, len);
> +	}
> +	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> +}
> +
> +bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	struct efi_unaccepted_memory *unaccepted;
> +	unsigned long flags;
> +	bool ret = false;
> +	u64 unit_size;
> +
> +	unaccepted = efi_get_unaccepted_table();
> +	if (!unaccepted)
> +		return false;
> +
> +	unit_size = unaccepted->unit_size;
> +
> +	/*
> +	 * Only care for the part of the range that is represented
> +	 * in the bitmap.
> +	 */
> +	if (start < unaccepted->phys_base)
> +		start = unaccepted->phys_base;

Same comment as above. Trimming start is fine?

> +	if (end < unaccepted->phys_base)
> +		return false;
> +
> +	/* Translate to offsets from the beginning of the bitmap */
> +	start -= unaccepted->phys_base;
> +	end -= unaccepted->phys_base;

Ditto as above.

> +
> +	/* Make sure not to overrun the bitmap */
> +	if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
> +		end = unaccepted->size * unit_size * BITS_PER_BYTE;

Ditto.

> +	spin_lock_irqsave(&unaccepted_memory_lock, flags);
> +	while (start < end) {
> +		if (test_bit(start / unit_size, unaccepted->bitmap)) {
> +			ret = true;
> +			break;

I have a faint memory we've had this before but you need to check
*every* bit in the unaccepted bitmap before returning true. Doh.

-- 
Regards/Gruss,
    Boris.

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