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Re: [PATCH v2] x86/hap: Defer NPT P2M TLB flushes
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Fri, 20 Mar 2026 09:44:39 +0000
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- Delivery-date: Fri, 20 Mar 2026 09:44:58 +0000
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On 3/19/26 2:06 PM, Roger Pau Monné wrote:
On Thu, Mar 19, 2026 at 11:40:41AM +0000, Ross Lagerwall wrote:
Like the EPT code, defer TLB flushes for NPT to reduce the number of
flushes and avoid holding the P2M lock while flushing. This can
substantially improve performance in some scenarios.
The cases where the TLB needs to be flushed without deferring are
already handled by the call to p2m_tlb_flush_sync() in p2m_free_ptp().
Suggested-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
In v2:
* Tweak commit message.
* Call guest_flush_tlb_mask() if the assertion fails.
xen/arch/x86/mm/hap/hap.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index a337752bf488..67137611d9db 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -814,15 +814,33 @@ static void cf_check hap_update_paging_modes(struct vcpu
*v)
static void cf_check
hap_write_p2m_entry_post(struct p2m_domain *p2m, unsigned int oflags)
{
- struct domain *d = p2m->domain;
+ if ( !(oflags & _PAGE_PRESENT) )
+ return;
+
+ if ( unlikely(!p2m->defer_flush) )
+ {
+ struct domain *d = p2m->domain;
As you are moving this around, and seeing that guest_flush_tlb_mask()
takes a const domain parameter, I think you could make this local
variable const. Possibly the same below with the other d local
variable.
Yes, that makes sense. Can the adjustment be done on commit if there is
no other feedback?
Thanks,
Ross
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