Re: [PATCH] MdePkg/BaseIoLibIntrinsicArmVirt ARM: avoid double word loads and stores

[Leif Lindholm <leif.lindholm@linaro.org>]

On Wed, Nov 07, 2018 at 02:38:37PM +0100, Ard Biesheuvel wrote:
> On 7 November 2018 at 14:13, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > BaseIoLibIntrinsicArmVirt was created to prevent LTO from merging
> > accesses to MMIO regions, resulting in instructions with multiple
> > output registers that KVM on ARM cannot emulate (since the exception
> > syndrome information that KVM relies on can only describe a single
> > output register)
> >
> > However, using double word loads on ARM amounts to the same thing,
> > and so code that relies on doing 64-bit MMIO to regions that are
> > emulated under KVM (such as the GICv3 TYPER register) will still
> > suffer from the original issue.
> >
> > So replace ldrd and strd with equivalent two instruction sequences.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> Please consider this patch with the hunk below appended

Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

> > ---
> >  MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S b/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S
> > index 3ad22bd5706d..0d802d6928d6 100644
> > --- a/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S
> > +++ b/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.S
> > @@ -125,7 +125,8 @@ ASM_PFX(MmioWrite32Internal):
> >  //  @return The value read.
> >  //
> >  ASM_PFX(MmioRead64Internal):
> > -  ldrd    r0, r1, [r0]
> > +  ldr     r1, [r0, #4]
> > +  ldr     r0, [r0]
> >    dmb
> >    bx      lr
> >
> > @@ -141,5 +142,6 @@ ASM_PFX(MmioRead64Internal):
> >  //
> >  ASM_PFX(MmioWrite64Internal):
> >    dmb     st
> > -  strd    r2, r3, [r0]
> > +  str     r2, [r0]
> > +  str     r3, [r0, #4]
> >    bx      lr
> 
> diff --git a/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.asm
> b/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.asm
> index e1a3d68a430c..deba8c1f0c59 100644
> --- a/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.asm
> +++ b/MdePkg/Library/BaseIoLibIntrinsic/Arm/ArmVirtMmio.asm
> @@ -127,7 +127,8 @@ MmioWrite32Internal
>  ;  @return The value read.
>  ;
>  MmioRead64Internal
> -  ldrd    r0, r1, [r0]
> +  ldr     r1, [r0, #4]
> +  ldr     r0, [r0]
>    dmb
>    bx      lr
> 
> @@ -143,7 +144,8 @@ MmioRead64Internal
>  ;
>  MmioWrite64Internal
>    dmb     st
> -  strd    r2, r3, [r0]
> +  str     r2, [r0]
> +  str     r3, [r0, #4]
>    bx      lr
> 
>    END