Re: [PATCH 04/10] s390/mm: force swiotlb for protected virtualization

Halil Pasic
2019-05-09T22:34:01Z

On Wed, 8 May 2019 15:15:40 +0200
Claudio Imbrenda <imbrenda@linux.ibm.com> wrote:

> On Fri, 26 Apr 2019 20:32:39 +0200
> Halil Pasic <pasic@linux.ibm.com> wrote:
>
> > On s390, protected virtualization guests have to use bounced I/O
> > buffers. That requires some plumbing.
> >
> > Let us make sure, any device that uses DMA API with direct ops
> > correctly is spared from the problems, that a hypervisor attempting
> > I/O to a non-shared page would bring.
> >
> > Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> > ---
> > arch/s390/Kconfig | 4 +++
> > arch/s390/include/asm/mem_encrypt.h | 18 +++++++++++++
> > arch/s390/mm/init.c | 50
> > +++++++++++++++++++++++++++++++++++++ 3 files changed, 72
> > insertions(+) create mode 100644 arch/s390/include/asm/mem_encrypt.h
> >
> > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> > index 1c3fcf19c3af..5500d05d4d53 100644
> > --- a/arch/s390/Kconfig
> > +++ b/arch/s390/Kconfig
> > @@ -1,4 +1,7 @@
> > # SPDX-License-Identifier: GPL-2.0
> > +config ARCH_HAS_MEM_ENCRYPT
> > + def_bool y
> > +
> > config MMU
> > def_bool y
> >
> > @@ -191,6 +194,7 @@ config S390
> > select ARCH_HAS_SCALED_CPUTIME
> > select VIRT_TO_BUS
> > select HAVE_NMI
> > + select SWIOTLB
> >
> >
> > config SCHED_OMIT_FRAME_POINTER
> > diff --git a/arch/s390/include/asm/mem_encrypt.h
> > b/arch/s390/include/asm/mem_encrypt.h new file mode 100644
> > index 000000000000..0898c09a888c
> > --- /dev/null
> > +++ b/arch/s390/include/asm/mem_encrypt.h
> > @@ -0,0 +1,18 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef S390_MEM_ENCRYPT_H__
> > +#define S390_MEM_ENCRYPT_H__
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#define sme_me_mask 0ULL
>
> This is rather ugly, but I understand why it's there
>

Nod.

> > +
> > +static inline bool sme_active(void) { return false; }
> > +extern bool sev_active(void);
> > +
> > +int set_memory_encrypted(unsigned long addr, int numpages);
> > +int set_memory_decrypted(unsigned long addr, int numpages);
> > +
> > +#endif /* __ASSEMBLY__ */
> > +
> > +#endif /* S390_MEM_ENCRYPT_H__ */
> > +
> > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > index 3e82f66d5c61..7e3cbd15dcfa 100644
> > --- a/arch/s390/mm/init.c
> > +++ b/arch/s390/mm/init.c
> > @@ -18,6 +18,7 @@
> > #include <linux/mman.h>
> > #include <linux/mm.h>
> > #include <linux/swap.h>
> > +#include <linux/swiotlb.h>
> > #include <linux/smp.h>
> > #include <linux/init.h>
> > #include <linux/pagemap.h>
> > @@ -29,6 +30,7 @@
> > #include <linux/export.h>
> > #include <linux/cma.h>
> > #include <linux/gfp.h>
> > +#include <linux/dma-mapping.h>
> > #include <asm/processor.h>
> > #include <linux/uaccess.h>
> > #include <asm/pgtable.h>
> > @@ -42,6 +44,8 @@
> > #include <asm/sclp.h>
> > #include <asm/set_memory.h>
> > #include <asm/kasan.h>
> > +#include <asm/dma-mapping.h>
> > +#include <asm/uv.h>
> >
> > pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
> >
> > @@ -126,6 +130,50 @@ void mark_rodata_ro(void)
> > pr_info("Write protected read-only-after-init data: %luk\n",
> > size >> 10); }
> >
> > +int set_memory_encrypted(unsigned long addr, int numpages)
> > +{
> > + int i;
> > +
> > + /* make all pages shared, (swiotlb, dma_free) */
>
> this is a copypaste typo, I think? (should be UNshared?)
> also, it doesn't make ALL pages unshared, but only those specified in
> the parameters

Right a copy paste error. Needs correction. The all was meant like all
pages in the range specified by the arguments. But it is better changed
since it turned out to be confusing.

>
> with this fixed:
> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
>

Thanks!

> > + for (i = 0; i < numpages; ++i) {
> > + uv_remove_shared(addr);
> > + addr += PAGE_SIZE;
> > + }
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(set_memory_encrypted);
> > +
> > +int set_memory_decrypted(unsigned long addr, int numpages)
> > +{
> > + int i;
> > + /* make all pages shared (swiotlb, dma_alloca) */
>
> same here with ALL
>
> > + for (i = 0; i < numpages; ++i) {
> > + uv_set_shared(addr);
> > + addr += PAGE_SIZE;
> > + }
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(set_memory_decrypted);
> > +
> > +/* are we a protected virtualization guest? */
> > +bool sev_active(void)
>
> this is also ugly. the correct solution would be probably to refactor
> everything, including all the AMD SEV code.... let's not go there
>

Nod. Maybe later.

> > +{
> > + return is_prot_virt_guest();
> > +}
> > +EXPORT_SYMBOL_GPL(sev_active);
> > +
> > +/* protected virtualization */
> > +static void pv_init(void)
> > +{
> > + if (!sev_active())
>
> can't you just use is_prot_virt_guest here?
>

Sure! I guess it would be less confusing. It is something I did not
remember to change when the interface for this provided by uv.h went
from sketchy to nice.

Thanks again!

Regards,
Halil

> > + return;
> > +
> > + /* make sure bounce buffers are shared */
> > + swiotlb_init(1);
> > + swiotlb_update_mem_attributes();
> > + swiotlb_force = SWIOTLB_FORCE;
> > +}
> > +
> > void __init mem_init(void)
> > {
> > cpumask_set_cpu(0, &init_mm.context.cpu_attach_mask);
> > @@ -134,6 +182,8 @@ void __init mem_init(void)
> > set_max_mapnr(max_low_pfn);
> > high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
> >
> > + pv_init();
> > +
> > /* Setup guest page hinting */
> > cmma_init();
> >
>