linux-kernel - Re: [PATCH v7 03/16] virt: sev-guest: Add SNP guest request structure

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Date: Sat, 27 Jan 2024 09:31:58 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, dionnaglaze@...gle.com, pgonda@...gle.com,
 seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v7 03/16] virt: sev-guest: Add SNP guest request structure

On 1/25/2024 5:29 PM, Borislav Petkov wrote:
> On Wed, Dec 20, 2023 at 08:43:45PM +0530, Nikunj A Dadhania wrote:
>> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio)
>> +int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
>> +			    struct snp_guest_request_ioctl *rio)
>>  {
>>  	struct ghcb_state state;
>>  	struct es_em_ctxt ctxt;
>>  	unsigned long flags;
>>  	struct ghcb *ghcb;
>> +	u64 exit_code;
> 
> Silly local vars. Just use req->exit_code everywhere instead.

Sure, will change.

> 
>>  	int ret;
>>  
>>  	rio->exitinfo2 = SEV_RET_NO_FW_CALL;
>> +	if (!req)
>> +		return -EINVAL;
> 
> Such tests are done under the variable which is assigned, not randomly.
> 
> Also, what's the point in testing req? Will that ever be NULL? What are
> you actually protecting against here?

Right, and in the later code, this is checked at snp_send_guest_request() API. So this is redundant.

>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 469e10d9bf35..5cafbd1c42cb 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -27,8 +27,7 @@
>>  
>>  #include <asm/svm.h>
>>  #include <asm/sev.h>
>> -
>> -#include "sev-guest.h"
>> +#include <asm/sev-guest.h>
>>  
>>  #define DEVICE_NAME	"sev-guest"
>>  
>> @@ -169,7 +168,7 @@ static struct aesgcm_ctx *snp_init_crypto(u8 *key, size_t keylen)
>>  	return ctx;
>>  }
>>  
>> -static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
>> +static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_req *guest_req)
> 
> So we call the request everywhere "req". But you've called it
> "guest_req" here because...

Yes, I was thinking about it and came up with this.

> 
>>  {
>>  	struct snp_guest_msg *resp = &snp_dev->secret_response;
>>  	struct snp_guest_msg *req = &snp_dev->secret_request;
> 
> ... there already is a "req" variable which is not a guest request thing
> but a guest message. So why don't you call it "req_msg" instead and the
> "resp" "resp_msg" so that it is clear what is what?
> 

This naming is much better, thanks.

> And then you can call the actual request var "req" and then the code
> becomes more readable...
> 
> ...
> 
>>  static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>>  {
>>  	struct snp_report_req *req = &snp_dev->req.report;
>> +	struct snp_guest_req guest_req = {0};
> 
> You have the same issue here.
> 
> If we aim at calling the local vars in every function the same, the code
> becomes automatically much more readable.
> 
> And so on...

Will change accordingly,

Regards
Nikunj