Re: [PATCH 3/5] Extend e820_table to hold information about memory encryption

[Dave Hansen <dave.hansen@intel.com>]

On 11/5/21 2:27 PM, Martin Fernandez wrote:
> Add a new member in e820_entry to hold whether an entry is able to do
> hardware memory encryption or not.

That's a bit sparse for what this is doing.  It covers the first hunk at
best.

> diff --git a/arch/x86/include/asm/e820/api.h b/arch/x86/include/asm/e820/api.h
> index e8f58ddd06d9..f3a09b6afca1 100644
> --- a/arch/x86/include/asm/e820/api.h
> +++ b/arch/x86/include/asm/e820/api.h
> @@ -18,6 +18,8 @@ extern void e820__range_add   (u64 start, u64 size, enum e820_type type);
>  extern u64  e820__range_update(u64 start, u64 size, enum e820_type old_type, enum e820_type new_type);
>  extern u64  e820__range_remove(u64 start, u64 size, enum e820_type old_type, bool check_type);
>  
> +extern void e820__mark_regions_as_crypto_capable(u64 start, u64 size);
> +
>  extern void e820__print_table(char *who);
>  extern int  e820__update_table(struct e820_table *table);
>  extern void e820__update_table_print(void);
> diff --git a/arch/x86/include/asm/e820/types.h b/arch/x86/include/asm/e820/types.h
> index 314f75d886d0..231c9ad9a9c3 100644
> --- a/arch/x86/include/asm/e820/types.h
> +++ b/arch/x86/include/asm/e820/types.h
> @@ -56,6 +56,7 @@ struct e820_entry {
>  	u64			addr;
>  	u64			size;
>  	enum e820_type		type;
> +	bool			crypto_capable;
>  } __attribute__((packed));
>  
>  /*
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index bc0657f0deed..3e0aaa5525e0 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -176,6 +176,7 @@ static void __init __e820__range_add(struct e820_table *table, u64 start, u64 si
>  	table->entries[x].addr = start;
>  	table->entries[x].size = size;
>  	table->entries[x].type = type;
> +	table->entries[x].crypto_capable = false;
>  	table->nr_entries++;
>  }
>  
> @@ -184,6 +185,19 @@ void __init e820__range_add(u64 start, u64 size, enum e820_type type)
>  	__e820__range_add(e820_table, start, size, type);
>  }
>  
> +void __init e820__mark_regions_as_crypto_capable(u64 start, u64 size)
> +{
> +	int i;
> +	u64 end = start + size;
> +
> +	for (i = 0; i < e820_table->nr_entries; i++) {
> +		struct e820_entry *const entry = &e820_table->entries[i];
> +
> +		if (entry->addr >= start && entry->addr + entry->size <= end)
> +			entry->crypto_capable = true;
> +	}
> +}

Looking at this in isolation, this is really tricky.  I have no idea
what this is _supposed_ to or expected to be doing.  It also makes me
wonder what happens when start/size don't line up exactly on an e820 entry.

>  static void __init e820_print_type(enum e820_type type)
>  {
>  	switch (type) {
> @@ -211,6 +225,8 @@ void __init e820__print_table(char *who)
>  			e820_table->entries[i].addr + e820_table->entries[i].size - 1);
>  
>  		e820_print_type(e820_table->entries[i].type);
> +		pr_cont("%s",
> +			e820_table->entries[i].crypto_capable ? "; crypto-capable" : "");

Am I missing something or should this just be:

	if (e820_table->entries[i].crypto_capable)
		pr_cont("; crypto-capable");

In general, I find code that retreats to the ternary form is almost
always doing something nasty.

>  		pr_cont("\n");
>  	}
>  }
> @@ -327,6 +343,8 @@ int __init e820__update_table(struct e820_table *table)
>  	unsigned long long last_addr;
>  	u32 new_nr_entries, overlap_entries;
>  	u32 i, chg_idx, chg_nr;
> +	bool current_crypto;
> +	bool last_crypto = false;
>  
>  	/* If there's only one memory region, don't bother: */
>  	if (table->nr_entries < 2)
> @@ -388,13 +406,17 @@ int __init e820__update_table(struct e820_table *table)
>  		 * 1=usable, 2,3,4,4+=unusable)
>  		 */
>  		current_type = 0;
> +		current_crypto = false;
>  		for (i = 0; i < overlap_entries; i++) {
> +			current_crypto = current_crypto || overlap_list[i]->crypto_capable;

No comment, eh?

This seems backwards to me.  If there are overlapping region and only
one is crypto-capable, shouldn't the whole thing become non-crypto-capable?

>  			if (overlap_list[i]->type > current_type)
>  				current_type = overlap_list[i]->type;
>  		}
>  
>  		/* Continue building up new map based on this information: */
> -		if (current_type != last_type || e820_nomerge(current_type)) {
> +		if (current_type != last_type ||
> +		    current_crypto != last_crypto ||
> +		    e820_nomerge(current_type)) {
>  			if (last_type != 0)	 {
>  				new_entries[new_nr_entries].size = change_point[chg_idx]->addr - last_addr;
>  				/* Move forward only if the new size was non-zero: */
> @@ -406,6 +428,9 @@ int __init e820__update_table(struct e820_table *table)
>  			if (current_type != 0)	{
>  				new_entries[new_nr_entries].addr = change_point[chg_idx]->addr;
>  				new_entries[new_nr_entries].type = current_type;
> +				new_entries[new_nr_entries].crypto_capable = current_crypto;
> +
> +				last_crypto = current_crypto;
>  				last_addr = change_point[chg_idx]->addr;
>  			}
>  			last_type = current_type;

The "current_crypto != last_crypto" checks seem to go with the
current_type/last_type checks.  I'm naively surprised that the
last_crypto assignment wasn't paired with the last_type assignment.

I kinda get the impression this was just quickly hacked in here.  It
seems like "crypto" and "type" are very closely related in how they are
being handled.  It's a shame they're not being managed in a common way.

> @@ -1321,7 +1346,10 @@ void __init e820__memblock_setup(void)
>  		if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN)
>  			continue;
>  
> -		memblock_add(entry->addr, entry->size);
> +		if (entry->crypto_capable)
> +			memblock_add_crypto_capable(entry->addr, entry->size);
> +		else
> +			memblock_add(entry->addr, entry->size);

Having a different memblock_add_foo() doesn't seem to be the way this is
done.  See:

	memblock_mark_hotplug();
or
	memblock_mark_mirror();

Shouldn't this be: memblock_mark_crypto()

By the way, how was this tested?