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KVM: x86/mmu: Add a helper function to check if an SPTE needs atomic write

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Move conditions in kvm_tdp_mmu_write_spte() to check if an SPTE should
be written atomically or not to a separate function.

This new function, kvm_tdp_mmu_spte_need_atomic_write(),  will be used
in future commits to optimize clearing bits in SPTEs.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230321220021.2119033-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Vipin Sharma 2023-03-21 15:00:09 -07:00 committed by Sean Christopherson
parent 50f1399845
commit 41e07665f1
1 changed files with 20 additions and 14 deletions
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34
arch/x86/kvm/mmu/tdp_iter.h
View File

@ -29,23 +29,29 @@ static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte)
WRITE_ONCE(*rcu_dereference(sptep), new_spte);
}
/*
* SPTEs must be modified atomically if they are shadow-present, leaf
* SPTEs, and have volatile bits, i.e. has bits that can be set outside
* of mmu_lock. The Writable bit can be set by KVM's fast page fault
* handler, and Accessed and Dirty bits can be set by the CPU.
*
* Note, non-leaf SPTEs do have Accessed bits and those bits are
* technically volatile, but KVM doesn't consume the Accessed bit of
* non-leaf SPTEs, i.e. KVM doesn't care if it clobbers the bit. This
* logic needs to be reassessed if KVM were to use non-leaf Accessed
* bits, e.g. to skip stepping down into child SPTEs when aging SPTEs.
*/
static inline bool kvm_tdp_mmu_spte_need_atomic_write(u64 old_spte, int level)
{
return is_shadow_present_pte(old_spte) &&
is_last_spte(old_spte, level) &&
spte_has_volatile_bits(old_spte);
}
static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
u64 new_spte, int level)
{
/*
* Atomically write the SPTE if it is a shadow-present, leaf SPTE with
* volatile bits, i.e. has bits that can be set outside of mmu_lock.
* The Writable bit can be set by KVM's fast page fault handler, and
* Accessed and Dirty bits can be set by the CPU.
*
* Note, non-leaf SPTEs do have Accessed bits and those bits are
* technically volatile, but KVM doesn't consume the Accessed bit of
* non-leaf SPTEs, i.e. KVM doesn't care if it clobbers the bit. This
* logic needs to be reassessed if KVM were to use non-leaf Accessed
* bits, e.g. to skip stepping down into child SPTEs when aging SPTEs.
*/
if (is_shadow_present_pte(old_spte) && is_last_spte(old_spte, level) &&
spte_has_volatile_bits(old_spte))
if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level))
return kvm_tdp_mmu_write_spte_atomic(sptep, new_spte);
__kvm_tdp_mmu_write_spte(sptep, new_spte);