On Mon, 12 Dec 2022, Julien Grall wrote: > From: Julien Grall <jgr...@amazon.com> > > Xen is currently not fully compliant with the Arm Arm because it will > switch the TTBR with the MMU on. > > In order to be compliant, we need to disable the MMU before > switching the TTBR. The implication is the page-tables should > contain an identity mapping of the code switching the TTBR. > > In most of the case we expect Xen to be loaded in low memory. I am aware > of one platform (i.e AMD Seattle) where the memory start above 512GB. > To give us some slack, consider that Xen may be loaded in the first 2TB > of the physical address space. > > The memory layout is reshuffled to keep the first two slots of the zeroeth > level free. Xen will now be loaded at (2TB + 2MB). This requires a slight > tweak of the boot code because XEN_VIRT_START cannot be used as an > immediate. > > This reshuffle will make trivial to create a 1:1 mapping when Xen is > loaded below 2TB. > > Signed-off-by: Julien Grall <jgr...@amazon.com> > --- > > Changes in v2: > - Reword the commit message > - Load Xen at 2TB + 2MB > - Update the documentation to reflect the new layout > --- > xen/arch/arm/arm64/head.S | 3 ++- > xen/arch/arm/include/asm/config.h | 34 +++++++++++++++++++++---------- > xen/arch/arm/mm.c | 11 +++++----- > 3 files changed, 31 insertions(+), 17 deletions(-) > > diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S > index ad014716db6f..23c2c7491db2 100644 > --- a/xen/arch/arm/arm64/head.S > +++ b/xen/arch/arm/arm64/head.S > @@ -607,7 +607,8 @@ create_page_tables: > * need an additional 1:1 mapping, the virtual mapping will > * suffice. > */ > - cmp x19, #XEN_VIRT_START > + ldr x0, =XEN_VIRT_START > + cmp x19, x0 > bne 1f > ret > 1: > diff --git a/xen/arch/arm/include/asm/config.h > b/xen/arch/arm/include/asm/config.h > index 6c1b762e976d..9fe6bfeeeb95 100644 > --- a/xen/arch/arm/include/asm/config.h > +++ b/xen/arch/arm/include/asm/config.h > @@ -72,15 +72,12 @@ > #include <xen/page-size.h> > > /* > - * Common ARM32 and ARM64 layout: > + * ARM32 layout: > * 0 - 2M Unmapped > * 2M - 4M Xen text, data, bss > * 4M - 6M Fixmap: special-purpose 4K mapping slots > * 6M - 10M Early boot mapping of FDT > - * 10M - 12M Livepatch vmap (if compiled in) > - * > - * ARM32 layout: > - * 0 - 12M <COMMON> > + * 10M - 12M Livepatch vmap (if compiled in) > * > * 32M - 128M Frametable: 24 bytes per page for 16GB of RAM > * 256M - 1G VMAP: ioremap and early_ioremap use this virtual address > @@ -90,8 +87,17 @@ > * 2G - 4G Domheap: on-demand-mapped > * > * ARM64 layout: > - * 0x0000000000000000 - 0x0000007fffffffff (512GB, L0 slot [0]) > - * 0 - 12M <COMMON> > + * 0x0000000000000000 - 0x00001fffffffffff (2TB, L0 slots [0..1]) > + *
Extra blank line > + * Reserved to identity map Xen > + * > + * 0x0000020000000000 - 0x000028fffffffff (512TB, L0 slot [2] > + * (Relative offsets) > + * 0 - 2M Unmapped > + * 2M - 4M Xen text, data, bss > + * 4M - 6M Fixmap: special-purpose 4K mapping slots > + * 6M - 10M Early boot mapping of FDT > + * 10M - 12M Livepatch vmap (if compiled in) > * > * 1G - 2G VMAP: ioremap and early_ioremap > * > @@ -107,7 +113,17 @@ > * Unused > */ > > +#ifdef CONFIG_ARM_32 > #define XEN_VIRT_START _AT(vaddr_t, MB(2)) > +#else > + > +#define SLOT0_ENTRY_BITS 39 > +#define SLOT0(slot) (_AT(vaddr_t,slot) << SLOT0_ENTRY_BITS) > +#define SLOT0_ENTRY_SIZE SLOT0(1) > + > +#define XEN_VIRT_START (SLOT0(2) + _AT(vaddr_t, MB(2))) > +#endif Sorry for the silly question and I apologize if I got the math wrong. 1<<39 is 512MB, so: slot0 is [0..512MB] slot1 is [512MB..1TB] slot2 is [1TB..1.5TB] slot3 is [1.5TB..2TB] slot4 is [2TB..2.5TB] So, if we want Xen just above 2TB we should use slot4? Which would be SLOT0(4) ? > #define XEN_VIRT_SIZE _AT(vaddr_t, MB(2)) > > #define FIXMAP_VIRT_START (XEN_VIRT_START + XEN_VIRT_SIZE) > @@ -164,10 +180,6 @@ > > #else /* ARM_64 */ > > -#define SLOT0_ENTRY_BITS 39 > -#define SLOT0(slot) (_AT(vaddr_t,slot) << SLOT0_ENTRY_BITS) > -#define SLOT0_ENTRY_SIZE SLOT0(1) > - > #define VMAP_VIRT_START GB(1) > #define VMAP_VIRT_SIZE GB(1) > > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c > index d0b1cf55f550..cc11f5c639e6 100644 > --- a/xen/arch/arm/mm.c > +++ b/xen/arch/arm/mm.c > @@ -153,7 +153,7 @@ static void __init __maybe_unused build_assertions(void) > #endif > /* Page table structure constraints */ > #ifdef CONFIG_ARM_64 > - BUILD_BUG_ON(zeroeth_table_offset(XEN_VIRT_START)); > + BUILD_BUG_ON(zeroeth_table_offset(XEN_VIRT_START) < 2); > #endif > BUILD_BUG_ON(first_table_offset(XEN_VIRT_START)); > #ifdef CONFIG_ARCH_MAP_DOMAIN_PAGE > @@ -498,10 +498,11 @@ void __init setup_pagetables(unsigned long > boot_phys_offset) > phys_offset = boot_phys_offset; > > #ifdef CONFIG_ARM_64 > - p = (void *) xen_pgtable; > - p[0] = pte_of_xenaddr((uintptr_t)xen_first); > - p[0].pt.table = 1; > - p[0].pt.xn = 0; > + pte = pte_of_xenaddr((uintptr_t)xen_first); > + pte.pt.table = 1; > + pte.pt.xn = 0; > + xen_pgtable[zeroeth_table_offset(XEN_VIRT_START)] = pte; > + > p = (void *) xen_first; > #else > p = (void *) cpu0_pgtable; > -- > 2.38.1 >
