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Commit 86935fc4 authored by Rusty Russell's avatar Rusty Russell
Browse files

lguest: map Switcher text whenever we allocate a new pagetable. 



It's always to same, so no need to put in the PTE every time we're
about to run.  Keep a flag to track whether the pagetable has the
Switcher entries allocated, and when allocating always initialize the
Switcher text PTE.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 3412b6ae

drivers/lguest/lg.h

+1 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 


struct pgdir {

	unsigned long gpgdir;

	bool switcher_mapped;

	pgd_t *pgdir;

};

drivers/lguest/page_tables.c

+32 −10
Original line number Diff line number Diff line
@@ -736,18 +736,39 @@ static unsigned int new_pgdir(struct lg_cpu *cpu, 


/*H:501

 * We do need the Switcher code mapped at all times, so we allocate that

 * part of the Guest page table here, and populate it when we're about to run

 * the guest.

 * part of the Guest page table here.  We map the Switcher code immediately,

 * but defer mapping of the guest register page and IDT/LDT etc page until

 * just before we run the guest in map_switcher_in_guest().

 *

 * We *could* do this setup in map_switcher_in_guest(), but at that point

 * we've interrupts disabled, and allocating pages like that is fraught: we

 * can't sleep if we need to free up some memory.

 */

static bool allocate_switcher_mapping(struct lg_cpu *cpu)

{

	int i;



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

		if (!find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,

			       CHECK_GPGD_MASK, _PAGE_TABLE))

		pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,

				       CHECK_GPGD_MASK, _PAGE_TABLE);

		if (!pte)

			return false;



		/*

		 * Map the switcher page if not already there.  It might

		 * already be there because we call allocate_switcher_mapping()

		 * in guest_set_pgd() just in case it did discard our Switcher

		 * mapping, but it probably didn't.

		 */

		if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {

			/* Get a reference to the Switcher page. */

			get_page(lg_switcher_pages[0]);

			/* Create a read-only, exectuable, kernel-style PTE */

			set_pte(pte,

				mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));

		}

	}

	cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;

	return true;

}
@@ -768,6 +789,7 @@ static void release_all_pagetables(struct lguest *lg) 
		/* Every PGD entry. */

		for (j = 0; j < PTRS_PER_PGD; j++)

			release_pgd(lg->pgdirs[i].pgdir + j);

		lg->pgdirs[i].switcher_mapped = false;

	}

}
@@ -827,9 +849,11 @@ void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable) 
	if (repin)

		pin_stack_pages(cpu);



	if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {

		if (!allocate_switcher_mapping(cpu))

			kill_guest(cpu, "Cannot populate switcher mapping");

	}

}

/*:*/



/*M:009
@@ -1076,10 +1100,8 @@ void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages) 
	struct page *percpu_switcher_page, *regs_page;

	pte_t *pte;



	/* Code page should always be mapped, and executable. */

	pte = find_spte(cpu, switcher_addr, false, 0, 0);

	get_page(lg_switcher_pages[0]);

	set_pte(pte, mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));

	/* Switcher page should always be mapped! */

	BUG_ON(!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped);



	/* Clear all the Switcher mappings for any other CPUs. */

	/* FIXME: This is dumb: update only when Host CPU changes. */