Hi,
On Mon, Apr 22, 2024 at 05:05:54PM +0100, Suzuki K Poulose wrote:
> On 22/04/2024 16:38, Alexandru Elisei wrote:
> > Hi,
> >
> > On Fri, Apr 12, 2024 at 11:33:43AM +0100, Suzuki K Poulose wrote:
> > > From: Joey Gouly <joey.gouly@xxxxxxx>
> > >
> > > A Realm must access any emulated I/O mappings with the PTE_NS_SHARED bit set.
> >
> > What entity requires that a realm must access I/O mappings with the
> > PTE_NS_SHARED bit set? Is that an architectural requirement? Or is it an
> > implementation choice made by the VMM and/or KVM?
>
> RMM spec. An MMIO access in the Protected IPA must be emulated by Realm
> world. If an MMIO access must be emulated by NS Host, it must be in the
> Unprotected IPA.
That's not exactly what I was asking. I was curious to know how a realm
knows if a MMIO access is emulated by the Realm, and thus it must use a
protected address, or it's emulated by the non-secure host, and it must use
an unprotected address.
Thanks,
Alex
>
> Technically, a VMM could create a memory map, where the NS emulated I/O
> are kept in the unprotected (upper) half.
>
> Or the VMM retains the current model and expects the Realm to use the
> "Unprotected" alias.
>
>
> Either way, applying the PTE_NS_SHARED attribute doesn't change anything and
> works for both the models, as far as the Realm is concerned.
>
>
> Suzuki
>
>
>
>
> >
> > Thanks,
> > Alex
> >
> > > This is modelled as a PTE attribute, but is actually part of the address.
> > >
> > > So, when MMU is disabled, the "physical address" must reflect this bit set. We
> > > access the UART early before the MMU is enabled. So, make sure the UART is
> > > accessed always with the bit set.
> > >
> > > Signed-off-by: Joey Gouly <joey.gouly@xxxxxxx>
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > > ---
> > > lib/arm/asm/pgtable.h | 5 +++++
> > > lib/arm/io.c | 24 +++++++++++++++++++++++-
> > > lib/arm64/asm/pgtable.h | 5 +++++
> > > 3 files changed, 33 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/lib/arm/asm/pgtable.h b/lib/arm/asm/pgtable.h
> > > index 350039ff..7e85e7c6 100644
> > > --- a/lib/arm/asm/pgtable.h
> > > +++ b/lib/arm/asm/pgtable.h
> > > @@ -112,4 +112,9 @@ static inline pte_t *pte_alloc(pmd_t *pmd, unsigned long addr)
> > > return pte_offset(pmd, addr);
> > > }
> > > +static inline unsigned long arm_shared_phys_alias(void *x)
> > > +{
> > > + return ((unsigned long)(x) | PTE_NS_SHARED);
> > > +}
> > > +
> > > #endif /* _ASMARM_PGTABLE_H_ */
> > > diff --git a/lib/arm/io.c b/lib/arm/io.c
> > > index 836fa854..127727e4 100644
> > > --- a/lib/arm/io.c
> > > +++ b/lib/arm/io.c
> > > @@ -15,6 +15,8 @@
> > > #include <asm/psci.h>
> > > #include <asm/spinlock.h>
> > > #include <asm/io.h>
> > > +#include <asm/mmu-api.h>
> > > +#include <asm/pgtable.h>
> > > #include "io.h"
> > > @@ -30,6 +32,24 @@ static struct spinlock uart_lock;
> > > static volatile u8 *uart0_base = UART_EARLY_BASE;
> > > bool is_pl011_uart;
> > > +static inline volatile u8 *get_uart_base(void)
> > > +{
> > > + /*
> > > + * The address of the UART base may be different
> > > + * based on whether we are running with/without
> > > + * MMU enabled.
> > > + *
> > > + * For realms, we must force to use the shared physical
> > > + * alias with MMU disabled, to make sure the I/O can
> > > + * be emulated.
> > > + * When the MMU is turned ON, the mappings are created
> > > + * appropriately.
> > > + */
> > > + if (mmu_enabled())
> > > + return uart0_base;
> > > + return (u8 *)arm_shared_phys_alias((void *)uart0_base);
> > > +}
> > > +
> > > static void uart0_init_fdt(void)
> > > {
> > > /*
> > > @@ -109,9 +129,11 @@ void io_init(void)
> > > void puts(const char *s)
> > > {
> > > + volatile u8 *uart_base = get_uart_base();
> > > +
> > > spin_lock(&uart_lock);
> > > while (*s)
> > > - writeb(*s++, uart0_base);
> > > + writeb(*s++, uart_base);
> > > spin_unlock(&uart_lock);
> > > }
> > > diff --git a/lib/arm64/asm/pgtable.h b/lib/arm64/asm/pgtable.h
> > > index 5b9f40b0..871c03e9 100644
> > > --- a/lib/arm64/asm/pgtable.h
> > > +++ b/lib/arm64/asm/pgtable.h
> > > @@ -28,6 +28,11 @@ extern unsigned long prot_ns_shared;
> > > */
> > > #define PTE_NS_SHARED (prot_ns_shared)
> > > +static inline unsigned long arm_shared_phys_alias(void *addr)
> > > +{
> > > + return ((unsigned long)addr | PTE_NS_SHARED);
> > > +}
> > > +
> > > /*
> > > * Highest possible physical address supported.
> > > */
> > > --
> > > 2.34.1
> > >
>
>
