linux-kernel - Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

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Date:   Mon, 21 Nov 2022 09:09:33 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when
 initializing TDX module as TDX memory


> >  
> > +struct tdx_memblock {
> > +	struct list_head list;
> > +	unsigned long start_pfn;
> 
> Why not use 'phys_addr_t'?

TDX memory must be page aligned, so start_pfn/end_pfn would be easier.

> 
> > +	unsigned long end_pfn;
> > +	int nid;
> > +};
> > +
> > 

[...]

> >  
> > +/* Check whether the given pfn range is covered by any CMR or not. */
> > +static bool pfn_range_covered_by_cmr(unsigned long start_pfn,
> > +				     unsigned long end_pfn)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < tdx_cmr_num; i++) {
> > +		struct cmr_info *cmr = &tdx_cmr_array[i];
> > +		unsigned long cmr_start_pfn;
> > +		unsigned long cmr_end_pfn;
> > +
> > +		cmr_start_pfn = cmr->base >> PAGE_SHIFT;
> > +		cmr_end_pfn = (cmr->base + cmr->size) >> PAGE_SHIFT;
> 
> Why not use PHYS_PFN() or PFN_DOWN()?  And PFN_PHYS() in reverse direction?

Didn't know them.  Will use them.


[...]

> > +
> > +/*
> > + * Add all memblock memory regions to the @tdx_memlist as TDX memory.
> > + * Must be called when get_online_mems() is called by the caller.
> > + */
> > +static int build_tdx_memory(void)
> > +{
> > +	unsigned long start_pfn, end_pfn;
> > +	int i, nid, ret;
> > +
> > +	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> > +		/*
> > +		 * The first 1MB may not be reported as TDX convertible
> > +		 * memory.  Manually exclude them as TDX memory.
> > +		 *
> > +		 * This is fine as the first 1MB is already reserved in
> > +		 * reserve_real_mode() and won't end up to ZONE_DMA as
> > +		 * free page anyway.
> > +		 */
> > +		start_pfn = max(start_pfn, (unsigned long)SZ_1M >> PAGE_SHIFT);
> > +		if (start_pfn >= end_pfn)
> > +			continue;
> 
> How about check whether first 1MB is reserved instead of depending on
> the corresponding code isn't changed?  Via for_each_reserved_mem_range()?

IIUC, some reserved memory can be freed to page allocator directly, i.e. kernel
init code/data.  I feel it's not safe to just treat reserved memory will never
be in page allocator.  Otherwise we have for_each_free_mem_range() can use.

[...]

> 
> > +/*
> > + * Check whether the given range is TDX memory.  Must be called between
> > + * mem_hotplug_begin()/mem_hotplug_done().
> 
> Must be called with mem_hotplug_lock write-locked.
> 

Will do.