Messages in this thread | | | Date | Thu, 2 Sep 2021 20:43:25 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH V2] KVM: X86: Move PTE present check from loop body to __shadow_walk_next() |
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On Fri, Aug 13, 2021, Lai Jiangshan wrote: > From: Lai Jiangshan <laijs@linux.alibaba.com> > > So far, the loop bodies already ensure the PTE is present before calling > __shadow_walk_next(): Some loop bodies simply exit with a !PRESENT > directly and some other loop bodies, i.e. FNAME(fetch) and __direct_map() > do not currently terminate their walks with a !PRESENT, but they get away > with it because they install present non-leaf SPTEs in the loop itself. > > But checking pte present in __shadow_walk_next() is a more prudent way of > programing and loop bodies will not need to always check it. It allows us > removing unneded is_shadow_present_pte() in the loop bodies. ^^^^^^^ unneeded
> > Terminating on !is_shadow_present_pte() is 100% the correct behavior, as > walking past a !PRESENT SPTE would lead to attempting to read a the next > level SPTE from a garbage iter->shadow_addr. Even some paths that do _not_ > currently have a !is_shadow_present_pte() in the loop body is Ok since > they will install present non-leaf SPTEs and the additinal present check ^^^^^^^^^ additional > is just an NOP. > > The checking result in __shadow_walk_next() will be propagated to > shadow_walk_okay() for being used in any for(;;) loop. > > Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> > ---
Nits aside,
Reviewed-by: Sean Christopherson <seanjc@google.com>
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