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From: Paul Durrant <xadimgnik@gmail.com>
Message-ID: <c14a3f2e-4cd1-4597-947b-a149e8ea52f9@xen.org>
Date: Fri, 9 Feb 2024 16:05:12 +0000
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Subject: Re: [PATCH v12 04/20] KVM: pfncache: add a mark-dirty helper
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To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
 David Woodhouse <dwmw2@infradead.org>, Shuah Khan <shuah@kernel.org>,
 kvm@vger.kernel.org, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
References: <20240115125707.1183-1-paul@xen.org>
 <20240115125707.1183-5-paul@xen.org> <ZcZLw1KGje61A9Yl@google.com>
Organization: Xen Project
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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.