linux-kernel - Re: [RFC 2/2] kvm: guest-side changes for tmem on KVM

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Date:	Mon, 19 Mar 2012 19:56:33 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Akshay Karle <akshay.a.karle@...il.com>,
	linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	kvm@...r.kernel.org, ashu tripathi <er.ashutripathi@...il.com>,
	nishant gulhane <nishant.s.gulhane@...il.com>,
	Shreyas Mahure <shreyas.mahure@...il.com>,
	amarmore2006 <amarmore2006@...il.com>,
	mahesh mohan <mahesh6490@...il.com>
Subject: Re: [RFC 2/2] kvm: guest-side changes for tmem on KVM

On 03/19/2012 07:49 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Mar 16, 2012 at 10:30:35AM +0530, Akshay Karle wrote:
> > >> +/* kvm tmem foundation ops/hypercalls */
> > >> +
> > >> +static inline int kvm_tmem_op(u32 tmem_cmd, u32 tmem_pool, struct tmem_oid oid,
> > >> +	u32 index, u32 tmem_offset, u32 pfn_offset, unsigned long pfn, u32 len, uint16_t cli_id)
> > >
> > > That is rather long list of arguments. Could you pass in a structure instead?
> > >
> > > Are you actually using all of the arguments in every call?
> > 
> > For different functions different parameters are used. If we want to reduce the number of arguments,
> > the tmem_ops structure can be created in the functions calling kvm_tmem_op instead of creating it here
> > and that can be passed, will make these changes in the next patch.
> > 
> > >> +{
> > >> +	struct tmem_ops op;
> > >> +	int rc = 0;
> > >> +	op.cmd = tmem_cmd;
> > >> +	op.pool_id = tmem_pool;
> > >> +	op.u.gen.oid[0] = oid.oid[0];
> > >> +	op.u.gen.oid[1] = oid.oid[1];
> > >> +	op.u.gen.oid[2] = oid.oid[2];
> > >> +	op.u.gen.index = index;
> > >> +	op.u.gen.tmem_offset = tmem_offset;
> > >> +	op.u.gen.pfn_offset = pfn_offset;
> > >> +	op.u.gen.pfn = pfn;
> > >> +	op.u.gen.len = len;
> > >> +	op.u.gen.cli_id = cli_id;
> > >> +	rc = kvm_hypercall1(KVM_HC_TMEM, virt_to_phys(&op));
> > >> +	rc = rc + 1000;
> > >
> > > Why the addition?
> > 
> > If you notice the host patch I had subtracted 1000 while passing the return value
> > in the kvm_emulate_hypercall function. This was to avoid the guest kernel panic due to
> > the return of a non-negative value by the kvm_hypercall. In order to get the original value
> > back I added 1000.
>
> Avi, is there a right way of doing this?

Why would the guest kernel panic due to the return of a non-negative value?

-- 
error compiling committee.c: too many arguments to function

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