On 7/8/21 10:30 AM, Dave Hansen wrote:
I was even thinking that you could use the pmd/pte entries that come
from the walk in dump_pagetable().
BTW, I think the snp_lookup_page_in_rmptable() interface is probably
wrong. It takes a 'struct page':
In some cases the caller already have 'struct page' so it was easier on
them. I can change it to snp_lookup_pfn_in_rmptable() to simplify the
things. In the cases where the caller already have 'struct page' will
simply do page_to_pfn().
+struct rmpentry *snp_lookup_page_in_rmptable(struct page *page, int *level)
but then immediately converts it to a paddr:
+ unsigned long phys = page_to_pfn(page) << PAGE_SHIFT;
If you just had it take a paddr, you wouldn't have to mess with all of
this pfn_valid() and phys_to_page() error checking.
Noted.
Or fix the snp_lookup_page_in_rmptable() interface, please.
Yes.
Let's capitalize "RMP" here, please.
Noted.
PGD 304b201067 P4D 304b201067 PUD 20c7f06063 PMD 20c8976063 PTE
80000020cee00163
RMPEntry paddr 0x20cee00000 [assigned=1 immutable=1 pagesize=0 gpa=0x0
^^^^^^^^^^
asid=0 vmsa=0 validated=0]
RMPEntry paddr 0x20cee00000 000000000000000f 8000000000000ffd
That's a good example, thanks!
But, it does make me think that we shouldn't be spitting out
"immutable". Should we call it "readonly" or something so that folks
have a better chance of figuring out what's wrong? Even better, should
we be looking specifically for X86_PF_RMP *and* immutable=1 and spitting
out something in english about it?
A write to an assigned page will cause the RMP violation. In this case,
the page happen to be firmware page hence the immutable bit was also
set. I am trying to use the field name as documented in the APM and
SEV-SNP firmware spec.
This also *looks* to be spitting out the same "RMPEntry paddr
0x20cee00000" more than once. Maybe we should just indent the extra
entries instead of repeating things. The high/low are missing a "0x"
prefix, they also don't have any kind of text label.
Noted, I will fix it.
I actually really like processing the fields. I think it's a good
investment to make the error messages as self-documenting as possible
and not require the poor souls who are decoding oopses to also keep each
vendor's architecture manuals at hand.
Sounds good, I will keep it as-is.
The reason for iterating through 2MB region is; if the faulting address
is not assigned in the RMP table, and page table walk level is 2MB then
one of entry within the large page is the root cause of the fault. Since
we don't know which entry hence I dump all the non-zero entries.
Logically you can figure this out though, right? Why throw 511 entries
at the console when we *know* they're useless?
Logically its going to be tricky to figure out which exact entry caused
the fault, hence I dump any non-zero entry. I understand it may dump
some useless.
There are two cases which we need to consider:
1) the faulting page is a guest private (aka assigned)
2) the faulting page is a hypervisor (aka shared)
We will be primarily seeing #1. In this case, we know its a assigned
page, and we can decode the fields.
The #2 will happen in rare conditions,
What rare conditions?
One such condition is RMP "in-use" bit is set; see the patch 20/40.
After applying the patch we should not see "in-use" bit set. If we run
into similar issues, a full RMP dump will greatly help debug.
if it happens, one of the undocumented bit in the RMP entry can
provide us some useful information hence we dump the raw values.
You're saying that there are things that can cause RMP faults that
aren't documented? That's rather nasty for your users, don't you think?
The "in-use" bit in the RMP entry caught me off guard. The AMD APM does
says that hardware sets in-use bit but it *never* explained in the
detail on how to check if the fault was due to in-use bit in the RMP
table. As I said, the documentation folks will be updating the RMP entry
to document the in-use bit. I hope we will not see any other
undocumented surprises, I am keeping my finger cross :)
I'd be fine if you want to define a mask of unknown bits and spit out to
the users that some unknown bits are set.
