linux-kernel - Re: [PATCH v12 04/20] KVM: pfncache: add a mark-dirty helper

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Message-ID: <c14a3f2e-4cd1-4597-947b-a149e8ea52f9@xen.org>
Date: Fri, 9 Feb 2024 16:05:12 +0000
From: Paul Durrant <xadimgnik@...il.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 David Woodhouse <dwmw2@...radead.org>, Shuah Khan <shuah@...nel.org>,
 kvm@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v12 04/20] KVM: pfncache: add a mark-dirty helper

On 09/02/2024 15:58, Sean Christopherson wrote:
> On Mon, Jan 15, 2024, Paul Durrant wrote:
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 7e7fd25b09b3..f3bb9e0a81fe 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -1399,6 +1399,17 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len);
>>    */
>>   void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
>>   
>> +/**
>> + * kvm_gpc_mark_dirty - mark a cached page as dirty.
>> + *
>> + * @gpc:	   struct gfn_to_pfn_cache object.
>> + */
>> +static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
>> +{
>> +	lockdep_assert_held(&gpc->lock);
>> +	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> 
> Can you opportunistically have this pre-check gpc->memslot?  __kvm_gpc_refresh()
> should nullify gpc->memslot when using an hva.  That way, you don't need to
> explicitly check for the "invalid gfn" case here (or you could, but WARN_ON_ONCE()
> if the memslot is non-NULL and the gfn is invalid?).

Ok, sure.