linux-kernel - Re: [PATCH v3] powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory

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Message-ID: <20200819170001.GC25497@char.us.oracle.com>
Date:   Wed, 19 Aug 2020 13:00:01 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3] powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere
 in memory

On Tue, Aug 18, 2020 at 07:11:26PM -0300, Thiago Jung Bauermann wrote:
> POWER secure guests (i.e., guests which use the Protection Execution
> Facility) need to use SWIOTLB to be able to do I/O with the hypervisor, but
> they don't need the SWIOTLB memory to be in low addresses since the
> hypervisor doesn't have any addressing limitation.
> 
> This solves a SWIOTLB initialization problem we are seeing in secure guests
> with 128 GB of RAM: they are configured with 4 GB of crashkernel reserved
> memory, which leaves no space for SWIOTLB in low addresses.
> 
> To do this, we use mostly the same code as swiotlb_init(), but allocate the
> buffer using memblock_alloc() instead of memblock_alloc_low().
> 
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>


> ---
>  arch/powerpc/include/asm/svm.h       |  4 ++++
>  arch/powerpc/mm/mem.c                |  6 +++++-
>  arch/powerpc/platforms/pseries/svm.c | 26 ++++++++++++++++++++++++++
>  3 files changed, 35 insertions(+), 1 deletion(-)
> 
> Changes from v2:
> - Panic if unable to allocate buffer, as suggested by Christoph.
> 
> Changes from v1:
> - Open-code swiotlb_init() in arch-specific code, as suggested by
>   Christoph.
> 
> diff --git a/arch/powerpc/include/asm/svm.h b/arch/powerpc/include/asm/svm.h
> index 85580b30aba4..7546402d796a 100644
> --- a/arch/powerpc/include/asm/svm.h
> +++ b/arch/powerpc/include/asm/svm.h
> @@ -15,6 +15,8 @@ static inline bool is_secure_guest(void)
>  	return mfmsr() & MSR_S;
>  }
>  
> +void __init svm_swiotlb_init(void);
> +
>  void dtl_cache_ctor(void *addr);
>  #define get_dtl_cache_ctor()	(is_secure_guest() ? dtl_cache_ctor : NULL)
>  
> @@ -25,6 +27,8 @@ static inline bool is_secure_guest(void)
>  	return false;
>  }
>  
> +static inline void svm_swiotlb_init(void) {}
> +
>  #define get_dtl_cache_ctor() NULL
>  
>  #endif /* CONFIG_PPC_SVM */
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index c2c11eb8dcfc..0f21bcb16405 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -50,6 +50,7 @@
>  #include <asm/swiotlb.h>
>  #include <asm/rtas.h>
>  #include <asm/kasan.h>
> +#include <asm/svm.h>
>  
>  #include <mm/mmu_decl.h>
>  
> @@ -290,7 +291,10 @@ void __init mem_init(void)
>  	 * back to to-down.
>  	 */
>  	memblock_set_bottom_up(true);
> -	swiotlb_init(0);
> +	if (is_secure_guest())
> +		svm_swiotlb_init();
> +	else
> +		swiotlb_init(0);
>  #endif
>  
>  	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
> diff --git a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platforms/pseries/svm.c
> index 40c0637203d5..81085eb8f225 100644
> --- a/arch/powerpc/platforms/pseries/svm.c
> +++ b/arch/powerpc/platforms/pseries/svm.c
> @@ -7,6 +7,7 @@
>   */
>  
>  #include <linux/mm.h>
> +#include <linux/memblock.h>
>  #include <asm/machdep.h>
>  #include <asm/svm.h>
>  #include <asm/swiotlb.h>
> @@ -34,6 +35,31 @@ static int __init init_svm(void)
>  }
>  machine_early_initcall(pseries, init_svm);
>  
> +/*
> + * Initialize SWIOTLB. Essentially the same as swiotlb_init(), except that it
> + * can allocate the buffer anywhere in memory. Since the hypervisor doesn't have
> + * any addressing limitation, we don't need to allocate it in low addresses.
> + */
> +void __init svm_swiotlb_init(void)
> +{
> +	unsigned char *vstart;
> +	unsigned long bytes, io_tlb_nslabs;
> +
> +	io_tlb_nslabs = (swiotlb_size_or_default() >> IO_TLB_SHIFT);
> +	io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
> +
> +	bytes = io_tlb_nslabs << IO_TLB_SHIFT;
> +
> +	vstart = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
> +	if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, false))
> +		return;
> +
> +	if (io_tlb_start)
> +		memblock_free_early(io_tlb_start,
> +				    PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
> +	panic("SVM: Cannot allocate SWIOTLB buffer");
> +}
> +
>  int set_memory_encrypted(unsigned long addr, int numpages)
>  {
>  	if (!PAGE_ALIGNED(addr))