Re: [PATCH 08/11] swiotlb: make the swiotlb_init interface more useful

Christoph Hellwig
2022-02-28T11:30:42Z

On Mon, Feb 28, 2022 at 02:53:39AM +0000, Michael Kelley (LINUX) wrote:
> From: Christoph Hellwig <hch@lst.de> Sent: Sunday, February 27, 2022 6:31 AM
> >
> > Pass a bool to pass if swiotlb needs to be enabled based on the
> > addressing needs and replace the verbose argument with a set of
> > flags, including one to force enable bounce buffering.
> >
> > Note that this patch removes the possibility to force xen-swiotlb
> > use using swiotlb=force on the command line on x86 (arm and arm64
> > never supported that), but this interface will be restored shortly.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > arch/arm/mm/init.c | 6 +----
> > arch/arm64/mm/init.c | 6 +----
> > arch/ia64/mm/init.c | 4 +--
> > arch/mips/cavium-octeon/dma-octeon.c | 2 +-
> > arch/mips/loongson64/dma.c | 2 +-
> > arch/mips/sibyte/common/dma.c | 2 +-
> > arch/powerpc/include/asm/swiotlb.h | 1 +
> > arch/powerpc/mm/mem.c | 3 ++-
> > arch/powerpc/platforms/pseries/setup.c | 3 ---
> > arch/riscv/mm/init.c | 8 +-----
> > arch/s390/mm/init.c | 3 +--
> > arch/x86/kernel/cpu/mshyperv.c | 8 ------
> > arch/x86/kernel/pci-dma.c | 15 ++++++-----
> > arch/x86/mm/mem_encrypt_amd.c | 3 ---
> > drivers/xen/swiotlb-xen.c | 4 +--
> > include/linux/swiotlb.h | 15 ++++++-----
> > include/trace/events/swiotlb.h | 29 ++++++++-------------
> > kernel/dma/swiotlb.c | 35 ++++++++++++++------------
> > 18 files changed, 56 insertions(+), 93 deletions(-)
>
> [snip]
>
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > index 5a99f993e6392..568274917f1cd 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -336,14 +336,6 @@ static void __init ms_hyperv_init_platform(void)
> > swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
> > #endif
> > }
> > -
> > -#ifdef CONFIG_SWIOTLB
> > - /*
> > - * Enable swiotlb force mode in Isolation VM to
> > - * use swiotlb bounce buffer for dma transaction.
> > - */
> > - swiotlb_force = SWIOTLB_FORCE;
> > -#endif
>
> With this code removed, it's not clear to me what forces the use of the
> swiotlb in a Hyper-V isolated VM. The code in pci_swiotlb_detect_4g() doesn't
> catch this case because cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)
> returns "false" in a Hyper-V guest. In the Hyper-V guest, it's only
> cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) that returns "true". I'm
> looking more closely at the meaning of the CC_ATTR_* values, and it may
> be that Hyper-V should also return "true" for CC_ATTR_MEM_ENCRYPT,
> but I don't think CC_ATTR_HOST_MEM_ENCRYPT should return "true".

Ok, I assumed that CC_ATTR_HOST_MEM_ENCRYPT returned true in this case.
I guess we just need to check for CC_ATTR_GUEST_MEM_ENCRYPT as well
there?