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Message-ID: <97945fb19901f6ec11c72b015f55f6bb42cbc7c1.camel@intel.com>
Subject: Re: [PATCH v5 05/22] x86/virt/tdx: Prevent hot-add driver managed
 memory
From:   Kai Huang <kai.huang@intel.com>
To:     Chao Gao <chao.gao@intel.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-mm@kvack.org, seanjc@google.com, pbonzini@redhat.com,
        dave.hansen@intel.com, len.brown@intel.com, tony.luck@intel.com,
        rafael.j.wysocki@intel.com, reinette.chatre@intel.com,
        dan.j.williams@intel.com, peterz@infradead.org, ak@linux.intel.com,
        kirill.shutemov@linux.intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com,
        isaku.yamahata@intel.com, akpm@linux-foundation.org
Date:   Fri, 24 Jun 2022 23:23:13 +1200
In-Reply-To: <20220624021200.GB15566@gao-cwp>
References: <cover.1655894131.git.kai.huang@intel.com>
         <173e1f9b2348f29e5f7d939855b8dd98625bcb35.1655894131.git.kai.huang@intel.com>
         <20220624021200.GB15566@gao-cwp>
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On Fri, 2022-06-24 at 10:12 +0800, Chao Gao wrote:
> On Wed, Jun 22, 2022 at 11:16:19PM +1200, Kai Huang wrote:
> > @@ -55,6 +55,7 @@
> > #include <asm/uv/uv.h>
> > #include <asm/setup.h>
> > #include <asm/ftrace.h>
> > +#include <asm/tdx.h>
> >=20
> > #include "mm_internal.h"
> >=20
> > @@ -972,6 +973,26 @@ int arch_add_memory(int nid, u64 start, u64 size,
> > 	return add_pages(nid, start_pfn, nr_pages, params);
> > }
> >=20
> > +int arch_memory_add_precheck(int nid, u64 start, u64 size, mhp_t mhp_f=
lags)
> > +{
> > +	if (!platform_tdx_enabled())
> > +		return 0;
>=20
> add a new cc attribute (if existing ones don't fit) for TDX host platform=
 and
> check the attribute here. So that the code here can be reused by other cc
> platforms if they have the same requirement.

Please see my explanation in the commit message:

The __weak arch-specific hook is used instead of a new CC_ATTR similar
to disable software CPU hotplug.  It is because some driver managed
memory resources may actually be TDX-capable (such as legacy PMEM, which
is underneath indeed RAM), and the arch-specific hook can be further
enhanced to allow those when needed.


--=20
Thanks,
-Kai