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Commit 2e917175 authored by Juergen Gross's avatar Juergen Gross Committed by David Vrabel
Browse files

xen: Speed up set_phys_to_machine() by using read-only mappings 



Instead of checking at each call of set_phys_to_machine() whether a
new p2m page has to be allocated due to writing an entry in a large
invalid or identity area, just map those areas read only and react
to a page fault on write by allocating the new page.

This change will make the common path with no allocation much
faster as it only requires a single write of the new mfn instead
of walking the address translation tables and checking for the
special cases.

Suggested-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
parent 054954eb

arch/x86/xen/p2m.c

+8 −6
Original line number Diff line number Diff line
@@ -70,6 +70,7 @@ 


#include <asm/cache.h>

#include <asm/setup.h>

#include <asm/uaccess.h>



#include <asm/xen/page.h>

#include <asm/xen/hypercall.h>
@@ -316,9 +317,9 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m) 
	paravirt_alloc_pte(&init_mm, __pa(p2m_identity_pte) >> PAGE_SHIFT);

	for (i = 0; i < PTRS_PER_PTE; i++) {

		set_pte(p2m_missing_pte + i,

			pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL));

			pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL_RO));

		set_pte(p2m_identity_pte + i,

			pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL));

			pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL_RO));

	}



	for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += chunk) {
@@ -365,7 +366,7 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m) 
				p2m_missing : p2m_identity;

			ptep = populate_extra_pte((unsigned long)(p2m + pfn));

			set_pte(ptep,

				pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL));

				pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL_RO));

			continue;

		}
@@ -624,6 +625,9 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn) 
		return true;

	}



	if (likely(!__put_user(mfn, xen_p2m_addr + pfn)))

		return true;



	ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level);

	BUG_ON(!ptep || level != PG_LEVEL_4K);
@@ -633,9 +637,7 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn) 
	if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity)))

		return mfn == IDENTITY_FRAME(pfn);



	xen_p2m_addr[pfn] = mfn;



	return true;

	return false;

}



bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)