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

Jason J. Herne
2019-05-09T18:05:20Z

> Subject: [PATCH 04/10] s390/mm: force swiotlb for protected virtualization
> Date: Fri, 26 Apr 2019 20:32:39 +0200
> From: Halil Pasic <pasic@linux.ibm.com>
> To: kvm@vger.kernel.org, linux-s390@vger.kernel.org, Cornelia Huck <cohuck@redhat.com>,
> Martin Schwidefsky <schwidefsky@de.ibm.com>, Sebastian Ott <sebott@linux.ibm.com>
> CC: Halil Pasic <pasic@linux.ibm.com>, virtualization@lists.linux-foundation.org, Michael
> S. Tsirkin <mst@redhat.com>, Christoph Hellwig <hch@infradead.org>, Thomas Huth
> <thuth@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Viktor Mihajlovski
> <mihajlov@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Janosch Frank
> <frankja@linux.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Farhan Ali
> <alifm@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>
>
> 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
> +
> +static inline bool sme_active(void) { return false; }
> +extern bool sev_active(void);
> +

I noticed this patch always returns false for sme_active. Is it safe to assume that
whatever fixups are required on x86 to deal with sme do not apply to s390?

> +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 comment should be "make all pages unshared"?

> +    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) */
> +    for (i = 0; i < numpages; ++i) {
> +        uv_set_shared(addr);
> +        addr += PAGE_SIZE;
> +    }
> +    return 0;
> +}
> +EXPORT_SYMBOL_GPL(set_memory_decrypted);

The addr arguments for the above functions appear to be referring to virtual addresses.
Would vaddr be a better name?

> +
> +/* are we a protected virtualization guest? */
> +bool sev_active(void)
> +{
> +    return is_prot_virt_guest();
> +}
> +EXPORT_SYMBOL_GPL(sev_active);
> +
> +/* protected virtualization */
> +static void pv_init(void)
> +{
> +    if (!sev_active())
> +        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();
>  -- 2.16.4
>
>

--
-- Jason J. Herne (jjherne@linux.ibm.com)