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

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Aug 19, 2024 at 02:19:10PM +0100, Steven Price wrote:
> +static bool rsi_version_matches(void)
> +{
> +	unsigned long ver_lower, ver_higher;
> +	unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
> +						&ver_lower,
> +						&ver_higher);
> +
> +	if (ret == SMCCC_RET_NOT_SUPPORTED)
> +		return false;
> +
> +	if (ret != RSI_SUCCESS) {
> +		pr_err("RME: RMM doesn't support RSI version %lu.%lu. Supported range: %lu.%lu-%lu.%lu\n",
> +		       RSI_ABI_VERSION_MAJOR, RSI_ABI_VERSION_MINOR,
> +		       RSI_ABI_VERSION_GET_MAJOR(ver_lower),
> +		       RSI_ABI_VERSION_GET_MINOR(ver_lower),
> +		       RSI_ABI_VERSION_GET_MAJOR(ver_higher),
> +		       RSI_ABI_VERSION_GET_MINOR(ver_higher));
> +		return false;
> +	}
> +
> +	pr_info("RME: Using RSI version %lu.%lu\n",
> +		RSI_ABI_VERSION_GET_MAJOR(ver_lower),
> +		RSI_ABI_VERSION_GET_MINOR(ver_lower));
> +
> +	return true;
> +}

I don't have the spec at hand now (on a plane) but given the possibility
of a 1.0 guest regressing on later RMM versions, I wonder whether we
should simply bail out if it's not an exact version match. I forgot what
the spec says about returned ranges (they were pretty confusing last
time I checked).

> +
> +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()?

-- 
Catalin