linux-kernel - Re: [PATCH 3/7] KVM-HV: KVM Steal time implementation

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Date:	Mon, 20 Jun 2011 16:38:54 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Anthony Liguori <aliguori@...ibm.com>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH 3/7] KVM-HV: KVM Steal time implementation

On Mon, Jun 20, 2011 at 09:42:31AM -0300, Glauber Costa wrote:
> On 06/20/2011 05:02 AM, Avi Kivity wrote:
> >On 06/20/2011 10:21 AM, Gleb Natapov wrote:
> >>On Sun, Jun 19, 2011 at 04:02:22PM +0300, Avi Kivity wrote:
> >>> On 06/19/2011 03:59 PM, Gleb Natapov wrote:
> >>> >On Sun, Jun 19, 2011 at 03:35:58PM +0300, Avi Kivity wrote:
> >>> >> On 06/15/2011 12:09 PM, Gleb Natapov wrote:
> >>> >> >>
> >>> >> >> Actually, I'd expect most read/writes to benefit from caching,
> >>no?
> >>> >> >> So why don't we just rename kvm_write_guest_cached() to
> >>> >> >> kvm_write_guest(), and the few places - if any - that need to
> >>force
> >>> >> >> transversing of the gfn mappings, get renamed to
> >>> >> >> kvm_write_guest_uncached ?
> >>> >> >>
> >>> >> >Good idea. I do not see any places where
> >>kvm_write_guest_uncached is
> >>> >> >needed from a brief look. Avi?
> >>> >> >
> >>> >>
> >>> >> kvm_write_guest_cached() needs something to supply the cache, and
> >>> >> needs recurring writes to the same location. Neither of these are
> >>> >> common (for example, instruction emulation doesn't have either).
> >>> >>
> >>> >Correct. Missed that. So what about changing steal time to use
> >>> >kvm_write_guest_cached()?
> >>>
> >>> Makes sense, definitely. Want to post read_guest_cached() as well?
> >>>
> >>Glauber can you write read_guest_cached() as part of your series (should
> >>be trivial), or do you want me to do it? I do not have a code to test it
> >>with though :)
> >
> >Yes.
> >
> >(you can write it, and Glauber can include it in the series)
> >
> Write it, handle me the patch, I'll include it and test it.

Only compile tested.

===
Introduce kvm_read_guest_cached() function in addition to write one we
already have.

Signed-off-by: Gleb Natapov <gleb@...hat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fa2321a..bf62c76 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1414,6 +1414,26 @@ int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 }
 EXPORT_SYMBOL_GPL(kvm_write_guest_cached);
 
+int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+			   void *data, unsigned long len)
+{
+	struct kvm_memslots *slots = kvm_memslots(kvm);
+	int r;
+
+	if (slots->generation != ghc->generation)
+		kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa);
+
+	if (kvm_is_error_hva(ghc->hva))
+		return -EFAULT;
+
+	r = __copy_from_user(data, (void __user *)ghc->hva, len);
+	if (r)
+		return -EFAULT;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_read_guest_cached);
+
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
 {
 	return kvm_write_guest_page(kvm, gfn, (const void *) empty_zero_page,
--
			Gleb.
--
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