From: David Woodhouse <dwmw2@infradead.org>
To: Paul Durrant <paul@xen.org>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 07/15] KVM: pfncache: include page offset in uhva and use it consistently
Date: Tue, 21 Nov 2023 22:35:42 +0000 [thread overview]
Message-ID: <5ffdf3ab49b047cd851289e5dc0697af0ffff45f.camel@infradead.org> (raw)
In-Reply-To: <20231121180223.12484-8-paul@xen.org>
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On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
> @@ -242,8 +242,7 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> }
>
> old_pfn = gpc->pfn;
> - old_khva = gpc->khva - offset_in_page(gpc->khva);
> - old_uhva = gpc->uhva;
> + old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
>
> /* If the userspace HVA is invalid, refresh that first */
> if (gpc->gpa != gpa || gpc->generation != slots->generation ||
> @@ -259,13 +258,25 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> ret = -EFAULT;
> goto out;
> }
There's a subtle behaviour change here, isn't there? I'd *really* like
you do say 'No functional change intended' where that is true, and then
the absence of that sentence in this one would be meaningful.
You are now calling hva_to_pfn_retry() even when the uhva page hasn't
changed. Which is harmless and probably not important, but IIUC fixable
by the addition of:
+ if (gpc->uhva != PAGE_ALIGN_DOWN(old_uhva))
> + hva_change = true;
> + } else {
> + /*
> + * No need to do any re-mapping if the only thing that has
> + * changed is the page offset. Just page align it to allow the
> + * new offset to be added in.
> + */
> + gpc->uhva = PAGE_ALIGN_DOWN(gpc->uhva);
> }
>
> + /* Note: the offset must be correct before calling hva_to_pfn_retry() */
> + gpc->uhva += page_offset;
> +
> /*
> * If the userspace HVA changed or the PFN was already invalid,
> * drop the lock and do the HVA to PFN lookup again.
> */
> - if (!gpc->valid || old_uhva != gpc->uhva) {
> + if (!gpc->valid || hva_change) {
> ret = hva_to_pfn_retry(gpc);
> } else {
> /*
> --
But I don't really think it's that important if you can come up with a
coherent justification for the change and note it in the commit
message. So either way:
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
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next prev parent reply other threads:[~2023-11-21 22:36 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 18:02 [PATCH v8 00/15] KVM: xen: update shared_info and vcpu_info handling Paul Durrant
2023-11-21 18:02 ` [PATCH v8 01/15] KVM: pfncache: Add a map helper function Paul Durrant
2023-11-21 18:02 ` [PATCH v8 02/15] KVM: pfncache: remove unnecessary exports Paul Durrant
2023-11-21 21:49 ` David Woodhouse
2023-11-22 8:44 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 03/15] KVM: xen: mark guest pages dirty with the pfncache lock held Paul Durrant
2023-11-21 21:49 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 04/15] KVM: pfncache: add a mark-dirty helper Paul Durrant
2023-11-21 18:02 ` [PATCH v8 05/15] KVM: pfncache: remove KVM_GUEST_USES_PFN usage Paul Durrant
2023-11-21 22:24 ` David Woodhouse
2023-11-27 23:36 ` Sean Christopherson
2023-11-21 18:02 ` [PATCH v8 06/15] KVM: pfncache: stop open-coding offset_in_page() Paul Durrant
2023-11-21 22:26 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 07/15] KVM: pfncache: include page offset in uhva and use it consistently Paul Durrant
2023-11-21 22:35 ` David Woodhouse [this message]
2023-11-22 9:29 ` Paul Durrant
2023-11-22 8:54 ` Xu Yilun
2023-11-22 9:12 ` David Woodhouse
2023-11-22 14:27 ` Xu Yilun
2023-11-22 15:42 ` David Woodhouse
2023-11-22 15:52 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 08/15] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA Paul Durrant
2023-11-21 22:47 ` David Woodhouse
2023-11-22 10:07 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 09/15] KVM: xen: allow shared_info to be mapped by fixed HVA Paul Durrant
2023-11-21 18:02 ` [PATCH v8 10/15] KVM: xen: allow vcpu_info " Paul Durrant
2023-11-21 18:02 ` [PATCH v8 11/15] KVM: selftests / xen: map shared_info using HVA rather than GFN Paul Durrant
2023-11-21 18:02 ` [PATCH v8 12/15] KVM: selftests / xen: re-map vcpu_info using HVA rather than GPA Paul Durrant
2023-11-21 18:02 ` [PATCH v8 13/15] KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability Paul Durrant
2023-11-21 18:02 ` [PATCH v8 14/15] KVM: xen: split up kvm_xen_set_evtchn_fast() Paul Durrant
2023-11-21 22:49 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 15/15] KVM: xen: allow vcpu_info content to be 'safely' copied Paul Durrant
2023-11-21 22:53 ` David Woodhouse
2023-11-22 10:39 ` David Woodhouse
2023-11-22 10:55 ` Paul Durrant
2023-11-22 11:25 ` David Woodhouse
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