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    SubjectRe: [RFC V1 3/5] x86: CVMs: Enable dynamic swiotlb by default for CVMs
    On Thu, Feb 1, 2024 at 5:50 PM Jeremi Piotrowski
    <jpiotrowski@linux.microsoft.com> wrote:
    >
    > On 12/01/2024 06:52, Vishal Annapurve wrote:
    > > CVMs used SWIOTLB for non-trusted IO using dma_map_* APIs. This series
    > > will ensure that dma_alloc_* API to also allocate from SWIOTLB pools.
    > > Initial size of SWIOTLB pool is decided using heuristics and has been
    > > working with CVM usecases so far.
    > >
    > > It's better to allow SWIOTLB to scale up on demand rather than keeping
    > > the size fixed to avoid failures with possibly increased usage of
    > > SWIOTLB with dma_alloc_* APIs allocating from SWIOTLB pools. This should
    > > also help in future with more devices getting used from CVMs for
    > > non-trusted IO.
    > >
    > > Signed-off-by: Vishal Annapurve <vannapurve@google.com>
    > > ---
    > > arch/x86/Kconfig | 2 ++
    > > 1 file changed, 2 insertions(+)
    > >
    > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    > > index 1566748f16c4..035c8a022c4c 100644
    > > --- a/arch/x86/Kconfig
    > > +++ b/arch/x86/Kconfig
    > > @@ -884,6 +884,7 @@ config INTEL_TDX_GUEST
    > > select X86_MEM_ENCRYPT
    > > select X86_MCE
    > > select UNACCEPTED_MEMORY
    > > + select SWIOTLB_DYNAMIC
    > > help
    > > Support running as a guest under Intel TDX. Without this support,
    > > the guest kernel can not boot or run under TDX.
    > > @@ -1534,6 +1535,7 @@ config AMD_MEM_ENCRYPT
    > > select ARCH_HAS_CC_PLATFORM
    > > select X86_MEM_ENCRYPT
    > > select UNACCEPTED_MEMORY
    > > + select SWIOTLB_DYNAMIC
    > > help
    > > Say yes to enable support for the encryption of system memory.
    > > This requires an AMD processor that supports Secure Memory
    >
    > What this does is unconditionally enable SWIOTLB_DYNAMIC for every kernel compiled
    > to support memory encryption, regardless of whether it runs inside a confidential guest.
    > I don't think that is what you intended.
    >

    Right, I will have to add a way to toggle this support dynamically in
    addition to having the support built in, based on more discussion
    around 2M allocations and dynamic scaling.

    > Best wishes,
    > Jeremi
    >
    >

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