linux-kernel - RE: [RFC PATCH V4 08/17] x86/hyperv: Initialize cpu and memory for sev-snp enlightened guest

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Message-ID: <BYAPR21MB16889228F8F5E91DFE43AF3CD79C9@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Mon, 17 Apr 2023 12:49:24 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        "luto@...nel.org" <luto@...nel.org>,
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Subject: RE: [RFC PATCH V4 08/17] x86/hyperv: Initialize cpu and memory for
 sev-snp enlightened guest

From: Tianyu Lan <ltykernel@...il.com> Sent: Sunday, April 16, 2023 12:21 AM
> 
> On 4/12/2023 10:39 PM, Michael Kelley (LINUX) wrote:
> >> +	/* Read processor number and memory layout. */
> >> +	processor_count = *(u32 *)__va(EN_SEV_SNP_PROCESSOR_INFO_ADDR);
> >> +	entry = (struct memory_map_entry *)(__va(EN_SEV_SNP_PROCESSOR_INFO_ADDR)
> >> +			+ sizeof(struct memory_map_entry));
> > Why is the first map entry being skipped?
> 
> The first entry is populated with processor count by Hyper-V.

Perhaps add a comment to acknowledge that the behavior
is a bit unexpected:

The 0th entry in the memory layout array contains just a 32-bit
processor count.  Read that value and then skip over the reminder
of the 0th entry.  Start processing memory_map_entry's with array
element 1.

Michael