From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: dirty all pages in kvm_write_guest_cached()
Date: Wed, 08 Apr 2015 12:43:15 +0200 [thread overview]
Message-ID: <55250643.3090402@redhat.com> (raw)
In-Reply-To: <20150408092611.GA2164@potion.brq.redhat.com>
On 08/04/2015 11:26, Radim Krčmář wrote:
> 2015-04-08 10:49+0200, Paolo Bonzini:
>> On 07/04/2015 22:34, Radim Krčmář wrote:
>>> We dirtied only one page because writes originally couldn't span more.
>>> Use improved syntax for '>> PAGE_SHIFT' while at it.
>>>
>>> Fixes: 8f964525a121 ("KVM: Allow cross page reads and writes from cached translations.")
>>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>>
>> Cross-page reads and writes should never get here; they have
>> ghc->memslot set to NULL and go through the slow path in kvm_write_guest.
>
> Only cross-memslot writes have NULL memslot.
The power of wrong comments...
Considering how kvm_gfn_to_hva_cache_init is used (one 1-byte field, two
4-byte fields, one 28-bytes struct that is 32-bytes aligned, one
32-bytes field that is in practice cacheline-aligned), I wonder if we
should just use ghc->memslot = NULL for cross page writes. This would
bypass the bug you are fixing here, and avoid worries about partial writes.
Paolo
next prev parent reply other threads:[~2015-04-08 10:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-07 20:34 [PATCH] KVM: dirty all pages in kvm_write_guest_cached() Radim Krčmář
2015-04-08 8:49 ` Paolo Bonzini
2015-04-08 9:26 ` Radim Krčmář
2015-04-08 10:43 ` Paolo Bonzini [this message]
2015-04-08 12:16 ` [PATCH] KVM: use slowpath for cross page cached accesses Radim Krčmář
2015-04-08 12:23 ` Paolo Bonzini
2015-04-09 0:18 ` Wanpeng Li
2015-05-02 12:23 ` Patch "KVM: use slowpath for cross page cached accesses" has been added to the 4.0-stable tree gregkh
2015-05-02 12:25 ` Patch "KVM: use slowpath for cross page cached accesses" has been added to the 3.19-stable tree gregkh
2015-05-02 12:28 ` Patch "KVM: use slowpath for cross page cached accesses" has been added to the 3.10-stable tree gregkh
2015-05-02 12:29 ` Patch "KVM: use slowpath for cross page cached accesses" has been added to the 3.14-stable tree gregkh
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