linux-kernel - Re: [PATCH v5 05/19] arm64: Detect if in a realm and set RIPAS RAM

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Message-ID: <bb69bde0-4564-49d6-bbd6-95bcbd4d272e@redhat.com>
Date: Tue, 10 Sep 2024 10:09:38 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>,
 Catalin Marinas <catalin.marinas@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev, Marc Zyngier
 <maz@...nel.org>, Will Deacon <will@...nel.org>,
 James Morse <james.morse@....com>, Oliver Upton <oliver.upton@...ux.dev>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
 Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun <alpergun@...gle.com>
Subject: Re: [PATCH v5 05/19] arm64: Detect if in a realm and set RIPAS RAM

On 8/31/24 1:54 AM, Steven Price wrote:
> On 26/08/2024 11:03, Catalin Marinas wrote:
>> On Mon, Aug 19, 2024 at 02:19:10PM +0100, Steven Price wrote:

[...]

>>> +
>>> +void __init arm64_rsi_setup_memory(void)
>>> +{
>>> +	u64 i;
>>> +	phys_addr_t start, end;
>>> +
>>> +	if (!is_realm_world())
>>> +		return;
>>> +
>>> +	/*
>>> +	 * Iterate over the available memory ranges and convert the state to
>>> +	 * protected memory. We should take extra care to ensure that we DO NOT
>>> +	 * permit any "DESTROYED" pages to be converted to "RAM".
>>> +	 *
>>> +	 * BUG_ON is used because if the attempt to switch the memory to
>>> +	 * protected has failed here, then future accesses to the memory are
>>> +	 * simply going to be reflected as a SEA (Synchronous External Abort)
>>> +	 * which we can't handle.  Bailing out early prevents the guest limping
>>> +	 * on and dying later.
>>> +	 */
>>> +	for_each_mem_range(i, &start, &end) {
>>> +		BUG_ON(rsi_set_memory_range_protected_safe(start, end));
>>> +	}
>>
>> Would it help debugging if we print the memory ranges as well rather
>> than just a BUG_ON()?
>>
> 
> Yes that would probably be useful - I'll fix that.
> 

One potential issue I'm seeing is WARN_ON() followed by BUG_ON(). They're a bit
duplicate. I would suggest to remove the WARN_ON() and print informative messages
in rsi_set_memory_range().

   setup_arch
   arm64_rsi_setup_memory                    // BUG_ON(error)
   rsi_set_memory_range_protected_safe
   rsi_set_memory_range                      // WARN_ON(error)

Thanks,
Gavin