Re: [PATCH 19/24] kvm: x86/mmu: Protect tdp_mmu_pages with a lock

Paolo Bonzini
2021-01-26T13:39:56Z

On 12/01/21 19:10, Ben Gardon wrote:
> + * May be acquired under the MMU lock in read mode or non-overlapping
> + * with the MMU lock.
> + */
> + spinlock_t tdp_mmu_pages_lock;

Is this correct? My understanding is that:

- you can take tdp_mmu_pages_lock from a shared MMU lock critical section

- you don't need to take tdp_mmu_pages_lock from an exclusive MMU lock
critical section, because you can't be concurrent with a shared critical
section

- but then, you can't take tdp_mmu_pages_lock outside the MMU lock,
because you could have

write_lock(mmu_lock)
spin_lock(tdp_mmu_pages_lock)
do tdp_mmu_pages_lock stuff !!! do tdp_mmu_pages_lock stuff
write_unlock(mmu_lock)
spin_unlock(tdp_mmu_pages_lock)

Paolo