linux-kernel - RE: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

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Date:   Mon, 1 Aug 2022 21:45:05 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

[AMD Official Use Only - General]

Hello Boris,

>> +static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level) {
>> +	unsigned long vaddr, paddr = pfn << PAGE_SHIFT;
>> +	struct rmpentry *entry, *large_entry;
>.> +
>> +	if (!pfn_valid(pfn))
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
>> +		return ERR_PTR(-ENXIO);

>That test should happen first.
Ok.

>> +	vaddr = rmptable_start + rmptable_page_offset(paddr);

>Wait, what does that macro do?

>It takes the physical address and gives the offset from the beginning of the RMP table in VA space?

>So why don't you do

>	entry = rmptable_entry(paddr)

>instead which simply gives you directly the entry in the RMP table with which you can work further?

>Instead of this macro doing half the work and then callers having to add the RMP start address and cast.

>And make it small function so that you can have typechecking too, while at it.

Ok, I will add a new corresponding rmptable_entry() function here, should be usable for getting the large
RMP entry below too.

>> +	if (unlikely(vaddr > rmptable_end))
>> +		return ERR_PTR(-ENXIO);
>> +
>> +	entry = (struct rmpentry *)vaddr;
>> +
>> +	/* Read a large RMP entry to get the correct page level used in RMP entry. */
>> +	vaddr = rmptable_start + rmptable_page_offset(paddr & PMD_MASK);
>> +	large_entry = (struct rmpentry *)vaddr;
>> +	*level = RMP_TO_X86_PG_LEVEL(rmpentry_pagesize(large_entry));
>> +
>> +	return entry;
>> +}
>> +
>> +/*
>> diff --git a/include/linux/sev.h b/include/linux/sev.h new file mode 
>> 100644 index 000000000000..1a68842789e1
>> --- /dev/null
>> +++ b/include/linux/sev.h

>Why is this header in the linux/ namespace and not in arch/x86/ ?

>All that stuff in here doesn't have any meaning outside of x86...

Yes, makes sense to move it to arch/x86.

Thanks,
Ashish