linux-kernel - Re: [RFC PATCH v2 0/3] KVM: allow mapping of compound tail pages for IO or PFNMAP mapping

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Message-ID: <ZdRg6pubbRSqWehY@yzhao56-desk.sh.intel.com>
Date: Tue, 20 Feb 2024 16:20:58 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <pbonzini@...hat.com>, <shuah@...nel.org>,
	<stevensd@...omium.org>
Subject: Re: [RFC PATCH v2 0/3] KVM: allow mapping of compound tail pages for
 IO or PFNMAP mapping

On Mon, Feb 12, 2024 at 07:07:25PM -0800, Sean Christopherson wrote:
> On Wed, Jan 03, 2024, Yan Zhao wrote:
> > This is a v2 for previous series [1] to allow mapping for compound tail
> > pages for IO or PFNMAP mapping.
> > 
> > Compared to v1, this version provides selftest to check functionality in
> > KVM to map memslots for MMIO BARs (VMAs with flag VM_IO | VM_PFNMAP), as
> > requested by Sean in [1].
> 
> Doh.  So I didn't intend for you to have to create a mock device just to be able
> to run a selftest.  I assumed it would be easy-ish to utilize an existing generic
> device.  I take it that's not the case?

The selftest requires a vma with flag (VM_IO | VM_PFNMAP) with non-reserved
pages as backend.

Without a mock device, I don't find a easy way to let the selftest take
effect.
So, I borrowed the way in "tools/testing/selftests/mm/hmm-tests.c" which
uses a mock driver in "lib/test_hmm.c".