Steven Rostedt
2007-Apr-18 17:50 UTC
[PATCH] Lguest32, use guest page tables to find paddr for emulated instructions
[Bug that was found by my previous patch] This patch allows things like modules, which don't have a direct __pa(EIP) mapping to do emulated instructions. Sure, the emulated instruction probably should be a paravirt_op, but this patch lets you at least boot a kernel that has modules needing emulated instructions. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Index: linux-2.6.21-rc5-mm2/drivers/lguest/core.c ==================================================================--- linux-2.6.21-rc5-mm2.orig/drivers/lguest/core.c +++ linux-2.6.21-rc5-mm2/drivers/lguest/core.c @@ -160,11 +160,14 @@ static int emulate_insn(struct lguest *l { u8 insn; unsigned int insnlen = 0, in = 0, shift = 0; - unsigned long physaddr = guest_pa(lg, lg->regs->eip); + unsigned long physaddr = lguest_find_guest_paddr(lg, lg->regs->eip); - /* This only works for addresses in linear mapping... */ - if (lg->regs->eip < lg->page_offset) + /* FIXME: Handle physaddr's that crosses pages (modules are in VM) */ + + /* did we actually find the physaddr? */ + if (physaddr == (unsigned long)-1UL) return 0; + lgread(lg, &insn, physaddr, 1); /* Operand size prefix means it's actually for ax. */ Index: linux-2.6.21-rc5-mm2/drivers/lguest/lg.h ==================================================================--- linux-2.6.21-rc5-mm2.orig/drivers/lguest/lg.h +++ linux-2.6.21-rc5-mm2/drivers/lguest/lg.h @@ -218,6 +218,7 @@ void guest_set_pte(struct lguest *lg, un void map_hypervisor_in_guest(struct lguest *lg, struct lguest_pages *pages); int demand_page(struct lguest *info, unsigned long cr2, int write); void pin_page(struct lguest *lg, unsigned long vaddr); +unsigned long lguest_find_guest_paddr(struct lguest *lg, unsigned long vaddr); /* lguest_user.c: */ int lguest_device_init(void); Index: linux-2.6.21-rc5-mm2/drivers/lguest/page_tables.c ==================================================================--- linux-2.6.21-rc5-mm2.orig/drivers/lguest/page_tables.c +++ linux-2.6.21-rc5-mm2/drivers/lguest/page_tables.c @@ -105,6 +105,25 @@ static spte_t gpte_to_spte(struct lguest return spte; } +unsigned long lguest_find_guest_paddr(struct lguest *lg, unsigned long vaddr) +{ + gpgd_t gpgd; + gpte_t gpte; + unsigned long gpte_ptr; + + gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr))); + if (!(gpgd.flags & _PAGE_PRESENT)) + return -1; + + gpte_ptr = gpte_addr(lg, gpgd, vaddr); + gpte = mkgpte(lgread_u32(lg, gpte_ptr)); + + if (!(gpte.flags & _PAGE_PRESENT)) + return -1; + + return (gpte.pfn << PAGE_SHIFT) | (vaddr & (PAGE_SIZE-1)); +} + /* FIXME: We hold reference to pages, which prevents them from being swapped. It'd be nice to have a callback when Linux wants to swap out. */
Rusty Russell
2007-Apr-18 17:50 UTC
[PATCH] Lguest32, use guest page tables to find paddr for emulated instructions
On Wed, 2007-04-04 at 15:07 -0400, Steven Rostedt wrote:> [Bug that was found by my previous patch] > > This patch allows things like modules, which don't have a direct > __pa(EIP) mapping to do emulated instructions. > > Sure, the emulated instruction probably should be a paravirt_op, but > this patch lets you at least boot a kernel that has modules needing > emulated instructions.Yeah, I haven't tried loading random modules but I can imagine this does happen (what module was it, BTW?) I used to have a function just like this, but managed to get rid of it. Hmm, perhaps we should have an "int lgread_virt_byte(u8 *)" which does the pgtable walk and read all in one? It won't be efficient, but it'll be more correct and maybe even fewer lines 8) Thanks for the patch! Rusty.