linux-kernel - Re: [PATCH v2 10/12] KVM: selftests / xen: map shared

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Message-ID: <e5cba995-7525-de56-fb0a-97697fe41cc7@xen.org>
Date:   Mon, 18 Sep 2023 14:24:20 +0100
From:   Paul Durrant <xadimgnik@...il.com>
To:     David Woodhouse <dwmw2@...radead.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Paul Durrant <pdurrant@...zon.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 10/12] KVM: selftests / xen: map shared_info using HVA
 rather than GFN

On 18/09/2023 14:19, David Woodhouse wrote:
> On Mon, 2023-09-18 at 11:21 +0000, Paul Durrant wrote:
>>
>> -                               ret = pthread_create(&thread, NULL, &juggle_shinfo_state, (void *)vm);
>> +                               if (has_shinfo_hva)
>> +                                       ret = pthread_create(&thread, NULL,
>> +                                                            &juggle_shinfo_state_hva, (void *)vm);
>> +                               else
>> +                                       ret = pthread_create(&thread, NULL,
>> +                                                            &juggle_shinfo_state_gfn, (void *)vm);
>>                                  TEST_ASSERT(ret == 0, "pthread_create() failed: %s", strerror(ret));
>>   
> 
> 
> This means you don't exercise the GFN-based path (which all current VMM
> implementations use) on newer kernels. Could you have a single
> juggle_shinfo_state() function as before, but make it repeatedly set
> and clear the shinfo using *both* HVA and GFN (if the former is
> available, of course).

The guidance is to use HVA if the feature is available; a VMM should not 
really be mixing and matching. That said, setting it either way should 
be equivalent.

> 
> While you're at it, it looks like the thread leaves the shinfo
> *deactivated*, which might come as a surprise to anyone who adds tests
> at the end near the existing TEST_DONE. Can we make it leave the shinfo
> *active* instead?

Ok.

   Paul