linux-kernel - Re: [PATCH v11 018/113] KVM: TDX: create/destroy VM structure

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Message-ID: <Y8F1uPsW56fVdhmC@google.com>
Date:   Fri, 13 Jan 2023 15:16:08 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Zhi Wang <zhi.wang.linux@...il.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH v11 018/113] KVM: TDX: create/destroy VM structure

On Fri, Jan 13, 2023, Zhi Wang wrote:
> On Thu, 12 Jan 2023 08:31:26 -0800 isaku.yamahata@...el.com wrote:
> > +static void tdx_reclaim_td_page(unsigned long td_page_pa)
> > +{
> > +	if (!td_page_pa)
> > +		return;
> > +	/*
> > +	 * TDCX are being reclaimed.  TDX module maps TDCX with HKID
> > +	 * assigned to the TD.  Here the cache associated to the TD
> > +	 * was already flushed by TDH.PHYMEM.CACHE.WB before here, So
> > +	 * cache doesn't need to be flushed again.
> > +	 */
> > +	if (WARN_ON(tdx_reclaim_page(td_page_pa, false, 0)))

The WARN_ON() can go, tdx_reclaim_page() has WARN_ON_ONCE() + pr_tdx_error() in
all error paths.

> > +		/* If reclaim failed, leak the page. */
> 
> Better add a FIXME: here as this has to be fixed later.

No, leaking the page is all KVM can reasonably do here.  An improved comment would
be helpful, but no code change is required.  tdx_reclaim_page() returns an error
if and only if there's an unexpected, fatal error, e.g. a SEAMCALL with bad params,
incorrect concurrency in KVM, a TDX Module bug, etc.  Retrying at a later point is
highly unlikely to be successful.