linux-kernel - Re: [PATCH v5 05/22] x86/virt/tdx: Prevent hot-add driver managed memory

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Date:   Fri, 24 Jun 2022 23:23:13 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, seanjc@...gle.com, pbonzini@...hat.com,
        dave.hansen@...el.com, len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com, akpm@...ux-foundation.org
Subject: Re: [PATCH v5 05/22] x86/virt/tdx: Prevent hot-add driver managed
 memory

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>
> > 
> > #include "mm_internal.h"
> > 
> > @@ -972,6 +973,26 @@ int arch_add_memory(int nid, u64 start, u64 size,
> > 	return add_pages(nid, start_pfn, nr_pages, params);
> > }
> > 
> > +int arch_memory_add_precheck(int nid, u64 start, u64 size, mhp_t mhp_flags)
> > +{
> > +	if (!platform_tdx_enabled())
> > +		return 0;
> 
> 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.


-- 
Thanks,
-Kai