| Message ID | 20190610193215.23704-14-julien.grall@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen/arm64: Rework head.S to make it more compliant with the Arm Arm | expand |
On Mon, 10 Jun 2019, Julien Grall wrote: > setup_fixmap() will setup the fixmap in the boot page tables in order to > use earlyprintk and also update the register x23 holding the address to > the UART. > > However, secondary CPUs are switching to the runtime page tables before > using the earlyprintk again. So settting up the fixmap in the boot pages > tables is pointless. Typo: settting Also, you could add that it is "impossible" to find ourselves in the position of needing earlyprintk for secondary CPUs before the runtime page tables are up, because it is done right after in the boot sequence. Reviewed-by: Stefano Stabellini <sstabellini@kernel.org> > This means most of setup_fixmap() is not necessary for the secondary > CPUs. The update of UART address is now moved out of setup_fixmap() and > duplicated in the CPU boot and secondary CPUs boot. Additionally, the > call to setup_fixmap() is removed from secondary CPUs boot. > > Signed-off-by: Julien Grall <julien.grall@arm.com> > --- > xen/arch/arm/arm64/head.S | 18 ++++++++---------- > 1 file changed, 8 insertions(+), 10 deletions(-) > > diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S > index 6be4af7579..192af3e8a2 100644 > --- a/xen/arch/arm/arm64/head.S > +++ b/xen/arch/arm/arm64/head.S > @@ -301,6 +301,10 @@ real_start_efi: > br x0 > primary_switched: > bl setup_fixmap > +#ifdef CONFIG_EARLY_PRINTK > + /* Use a virtual address to access the UART. */ > + ldr x23, =EARLY_UART_VIRTUAL_ADDRESS > +#endif > b launch > ENDPROC(real_start) > > @@ -343,8 +347,6 @@ GLOBAL(init_secondary) > ldr x0, =secondary_switched > br x0 > secondary_switched: > - bl setup_fixmap > - > /* > * Non-boot CPUs need to move on to the proper pagetables, which were > * setup in init_secondary_pagetables. > @@ -361,6 +363,10 @@ secondary_switched: > dsb sy /* Ensure completion of TLB flush */ > isb > > +#ifdef CONFIG_EARLY_PRINTK > + /* Use a virtual address to access the UART. */ > + ldr x23, =EARLY_UART_VIRTUAL_ADDRESS > +#endif > b launch > ENDPROC(init_secondary) > > @@ -631,10 +637,6 @@ setup_fixmap: > * don't need the 1:1 map any more */ > dsb sy > #if defined(CONFIG_EARLY_PRINTK) /* Fixmap is only used by early printk */ > - /* Non-boot CPUs don't need to rebuild the fixmap itself, just > - * the mapping from boot_second to xen_fixmap */ > - cbnz x22, 1f > - > /* Add UART to the fixmap table */ > ldr x1, =xen_fixmap /* x1 := vaddr (xen_fixmap) */ > lsr x2, x23, #THIRD_SHIFT > @@ -642,7 +644,6 @@ setup_fixmap: > mov x3, #PT_DEV_L3 > orr x2, x2, x3 /* x2 := 4K dev map including UART */ > str x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's slot */ > -1: > > /* Map fixmap into boot_second */ > ldr x4, =boot_second /* x4 := vaddr (boot_second) */ > @@ -652,9 +653,6 @@ setup_fixmap: > ldr x1, =FIXMAP_ADDR(0) > lsr x1, x1, #(SECOND_SHIFT - 3) /* x1 := Slot for FIXMAP(0) */ > str x2, [x4, x1] /* Map it in the fixmap's slot */ > - > - /* Use a virtual address to access the UART. */ > - ldr x23, =EARLY_UART_VIRTUAL_ADDRESS > #endif > > /* > -- > 2.11.0 >
Hi, On 6/26/19 7:51 PM, Stefano Stabellini wrote: > On Mon, 10 Jun 2019, Julien Grall wrote: >> setup_fixmap() will setup the fixmap in the boot page tables in order to >> use earlyprintk and also update the register x23 holding the address to >> the UART. >> >> However, secondary CPUs are switching to the runtime page tables before >> using the earlyprintk again. So settting up the fixmap in the boot pages >> tables is pointless. > > Typo: settting ok. > > Also, you could add that it is "impossible" to find ourselves in the > position of needing earlyprintk for secondary CPUs before the runtime > page tables are up, because it is done right after in the boot sequence. It is kind of implied by the comment and the code below. But I can clearly state it. > > Reviewed-by: Stefano Stabellini <sstabellini@kernel.org> Cheers,
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S index 6be4af7579..192af3e8a2 100644 --- a/xen/arch/arm/arm64/head.S +++ b/xen/arch/arm/arm64/head.S @@ -301,6 +301,10 @@ real_start_efi: br x0 primary_switched: bl setup_fixmap +#ifdef CONFIG_EARLY_PRINTK + /* Use a virtual address to access the UART. */ + ldr x23, =EARLY_UART_VIRTUAL_ADDRESS +#endif b launch ENDPROC(real_start) @@ -343,8 +347,6 @@ GLOBAL(init_secondary) ldr x0, =secondary_switched br x0 secondary_switched: - bl setup_fixmap - /* * Non-boot CPUs need to move on to the proper pagetables, which were * setup in init_secondary_pagetables. @@ -361,6 +363,10 @@ secondary_switched: dsb sy /* Ensure completion of TLB flush */ isb +#ifdef CONFIG_EARLY_PRINTK + /* Use a virtual address to access the UART. */ + ldr x23, =EARLY_UART_VIRTUAL_ADDRESS +#endif b launch ENDPROC(init_secondary) @@ -631,10 +637,6 @@ setup_fixmap: * don't need the 1:1 map any more */ dsb sy #if defined(CONFIG_EARLY_PRINTK) /* Fixmap is only used by early printk */ - /* Non-boot CPUs don't need to rebuild the fixmap itself, just - * the mapping from boot_second to xen_fixmap */ - cbnz x22, 1f - /* Add UART to the fixmap table */ ldr x1, =xen_fixmap /* x1 := vaddr (xen_fixmap) */ lsr x2, x23, #THIRD_SHIFT @@ -642,7 +644,6 @@ setup_fixmap: mov x3, #PT_DEV_L3 orr x2, x2, x3 /* x2 := 4K dev map including UART */ str x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's slot */ -1: /* Map fixmap into boot_second */ ldr x4, =boot_second /* x4 := vaddr (boot_second) */ @@ -652,9 +653,6 @@ setup_fixmap: ldr x1, =FIXMAP_ADDR(0) lsr x1, x1, #(SECOND_SHIFT - 3) /* x1 := Slot for FIXMAP(0) */ str x2, [x4, x1] /* Map it in the fixmap's slot */ - - /* Use a virtual address to access the UART. */ - ldr x23, =EARLY_UART_VIRTUAL_ADDRESS #endif /*
setup_fixmap() will setup the fixmap in the boot page tables in order to use earlyprintk and also update the register x23 holding the address to the UART. However, secondary CPUs are switching to the runtime page tables before using the earlyprintk again. So settting up the fixmap in the boot pages tables is pointless. This means most of setup_fixmap() is not necessary for the secondary CPUs. The update of UART address is now moved out of setup_fixmap() and duplicated in the CPU boot and secondary CPUs boot. Additionally, the call to setup_fixmap() is removed from secondary CPUs boot. Signed-off-by: Julien Grall <julien.grall@arm.com> --- xen/arch/arm/arm64/head.S | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-)