linux-kernel - Re: [RFC V3 PATCH 3/6] selftests: kvm: ucall: Allow querying ucall pool gpa

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Message-ID: <CAGtprH_XSCXZDroGUnL3H1CwcsbH_A_NDn8B4P2xfpSYGqKmqw@mail.gmail.com>
Date:   Fri, 14 Oct 2022 15:03:48 +0530
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        shuah@...nel.org, yang.zhong@...el.com, drjones@...hat.com,
        ricarkol@...gle.com, aaronlewis@...gle.com, wei.w.wang@...el.com,
        kirill.shutemov@...ux.intel.com, corbet@....net, hughd@...gle.com,
        jlayton@...nel.org, bfields@...ldses.org,
        akpm@...ux-foundation.org, chao.p.peng@...ux.intel.com,
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        mizhang@...gle.com, bgardon@...gle.com
Subject: Re: [RFC V3 PATCH 3/6] selftests: kvm: ucall: Allow querying ucall
 pool gpa

On Fri, Oct 7, 2022 at 1:32 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Fri, Aug 19, 2022, Vishal Annapurve wrote:
> > Add a helper to query guest physical address for ucall pool
> > so that guest can mark the page as accessed shared or private.
> >
> > Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
> > ---
>
> This should be handled by the SEV series[*].  Can you provide feedback on that
> series if having a generic way to map the ucall address as shared won't work?
>
> [*] https://lore.kernel.org/all/20220829171021.701198-1-pgonda@google.com

Based on the SEV series you referred to, selftests are capable of
accessing ucall pool memory by having encryption bit cleared (as set
by guest pagetables) as allowed by generic API vm_vaddr_alloc_shared.
This change is needed in the context of fd based private memory where
guest (specifically non-confidential/sev guests) code in the selftests
will have to explicitly indicate that ucall pool address range will be
accessed by guest as shared.