linux-kernel - Re: [PATCH v3 0/6] KVM: Dirty ring fixes and cleanups

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Message-ID: <aCzUIsn1ZF2lEOJ-@x1.local>
Date: Tue, 20 May 2025 15:12:34 -0400
From: Peter Xu <peterx@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Yan Zhao <yan.y.zhao@...el.com>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	Binbin Wu <binbin.wu@...ux.intel.com>,
	James Houghton <jthoughton@...gle.com>,
	Pankaj Gupta <pankaj.gupta@....com>
Subject: Re: [PATCH v3 0/6]  KVM: Dirty ring fixes and cleanups

On Fri, May 16, 2025 at 02:35:34PM -0700, Sean Christopherson wrote:
> Sean Christopherson (6):
>   KVM: Bound the number of dirty ring entries in a single reset at
>     INT_MAX
>   KVM: Bail from the dirty ring reset flow if a signal is pending
>   KVM: Conditionally reschedule when resetting the dirty ring
>   KVM: Check for empty mask of harvested dirty ring entries in caller
>   KVM: Use mask of harvested dirty ring entries to coalesce dirty ring
>     resets
>   KVM: Assert that slots_lock is held when resetting per-vCPU dirty
>     rings

For the last one, I'd think it's majorly because of the memslot accesses
(or CONFIG_LOCKDEP=y should yell already on resets?).  The "serialization
of concurrent RESETs" part could be a good side effect.  After all, the
dirty rings rely a lot on the userspace to do right things.. for example,
the userspace better also remember to reset before any slot changes, or
it's possible to collect a dirty pfn with a slot index that was already
removed and reused with a new one..

Maybe we could switch the sentences there in the comment of last patch, but
not a huge deal.

Reviewed-by: Peter Xu <peterx@...hat.com>

Thanks!

-- 
Peter Xu