[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/ept: fix shattering of special pages
On 27.06.2022 12:01, Roger Pau Monne wrote: > The current logic in epte_get_entry_emt() will split any page marked > as special with order greater than zero, without checking whether the > super page is all special. > > Fix this by only splitting the page only if it's not all marked as > special, in order to prevent unneeded super page shuttering. > > Fixes: ca24b2ffdb ('x86/hvm: set 'ipat' in EPT for special pages') > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > --- > Cc: Paul Durrant <paul@xxxxxxx> > --- > It would seem weird to me to have a super page entry in EPT with > ranges marked as special and not the full page. I guess it's better > to be safe, but I don't see an scenario where we could end up in that > situation. > > I've been trying to find a clarification in the original patch > submission about how it's possible to have such super page EPT entry, > but haven't been able to find any justification. I think the loop there was added "just in case", whereas in reality it was only single special pages that would ever be mapped. So ... > Might be nice to expand the commit message as to why it's possible to > have such mixed super page entries that would need splitting. ... there may not be anything to add. I don't mind this being re-done, hence Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> Yet I'm not sure I understand what case this actually fixes (and hence why you did add a Fixes: tag) - are there cases where non- order-0 special pages are mapped in reality? As to the Fixes: tag - I think we mean to follow Linux there and hence want 12-digit hashes to be specified. See also docs/process/sending-patches.pandoc. (But no need to resend just for this.) Jan
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