Commit 41f2e477 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge
Browse files

xen: add support for PAT 



Convert Linux PAT entries into Xen ones when constructing ptes.  Linux
doesn't use _PAGE_PAT for ptes, so the only difference in the first 4
entries is that Linux uses _PAGE_PWT for WC, whereas Xen (and default)
use it for WT.

xen_pte_val does the inverse conversion.

We hard-code assumptions about Linux's current PAT layout, but a
warning on the wrmsr to MSR_IA32_CR_PAT should point out any problems.
If necessary we could go to a more general table-based conversion between
Linux and Xen PAT entries.

hugetlbfs poses a problem at the moment, the x86 architecture uses the
same flag for _PAGE_PAT and _PAGE_PSE, which changes meaning depending
on which pagetable level we're using.  At the moment this should be OK
so long as nobody tries to do a pte_val on a hugetlbfs pte.

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
parent 2f7acb20

arch/x86/xen/enlighten.c

+5 −0
Original line number Diff line number Diff line
@@ -829,6 +829,11 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high) 
		   Xen console noise. */

		break;



	case MSR_IA32_CR_PAT:

		if (smp_processor_id() == 0)

			xen_set_pat(((u64)high << 32) | low);

		break;



	default:

		ret = native_write_msr_safe(msr, low, high);

	}

arch/x86/xen/mmu.c

+50 −3
Original line number Diff line number Diff line
@@ -55,6 +55,7 @@ 
#include <asm/e820.h>

#include <asm/linkage.h>

#include <asm/page.h>

#include <asm/pat.h>



#include <asm/xen/hypercall.h>

#include <asm/xen/hypervisor.h>
@@ -780,10 +781,18 @@ static pteval_t iomap_pte(pteval_t val) 


pteval_t xen_pte_val(pte_t pte)

{

	if (xen_initial_domain() && (pte.pte & _PAGE_IOMAP))

		return pte.pte;

	pteval_t pteval = pte.pte;



	return pte_mfn_to_pfn(pte.pte);

	/* If this is a WC pte, convert back from Xen WC to Linux WC */

	if ((pteval & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)) == _PAGE_PAT) {

		WARN_ON(!pat_enabled);

		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;

	}



	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))

		return pteval;



	return pte_mfn_to_pfn(pteval);

}

PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
@@ -793,10 +802,48 @@ pgdval_t xen_pgd_val(pgd_t pgd) 
}

PV_CALLEE_SAVE_REGS_THUNK(xen_pgd_val);



/*

 * Xen's PAT setup is part of its ABI, though I assume entries 6 & 7

 * are reserved for now, to correspond to the Intel-reserved PAT

 * types.

 *

 * We expect Linux's PAT set as follows:

 *

 * Idx  PTE flags        Linux    Xen    Default

 * 0                     WB       WB     WB

 * 1            PWT      WC       WT     WT

 * 2        PCD          UC-      UC-    UC-

 * 3        PCD PWT      UC       UC     UC

 * 4    PAT              WB       WC     WB

 * 5    PAT     PWT      WC       WP     WT

 * 6    PAT PCD          UC-      UC     UC-

 * 7    PAT PCD PWT      UC       UC     UC

 */



void xen_set_pat(u64 pat)

{

	/* We expect Linux to use a PAT setting of

	 * UC UC- WC WB (ignoring the PAT flag) */

	WARN_ON(pat != 0x0007010600070106ull);

}



pte_t xen_make_pte(pteval_t pte)

{

	phys_addr_t addr = (pte & PTE_PFN_MASK);



	/* If Linux is trying to set a WC pte, then map to the Xen WC.

	 * If _PAGE_PAT is set, then it probably means it is really

	 * _PAGE_PSE, so avoid fiddling with the PAT mapping and hope

	 * things work out OK...

	 *

	 * (We should never see kernel mappings with _PAGE_PSE set,

	 * but we could see hugetlbfs mappings, I think.).

	 */

	if (pat_enabled && !WARN_ON(pte & _PAGE_PAT)) {

		if ((pte & (_PAGE_PCD | _PAGE_PWT)) == _PAGE_PWT)

			pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;

	}



	/*

	 * Unprivileged domains are allowed to do IOMAPpings for

	 * PCI passthrough, but not map ISA space.  The ISA

arch/x86/xen/xen-ops.h

+2 −0
Original line number Diff line number Diff line
@@ -32,6 +32,8 @@ void xen_ident_map_ISA(void); 
void xen_reserve_top(void);

extern unsigned long xen_max_p2m_pfn;



void xen_set_pat(u64);



char * __init xen_memory_setup(void);

void __init xen_arch_setup(void);

void __init xen_init_IRQ(void);

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