| Message ID | 3f1795bc1dad1d0510a9d24a168ecd5d83666507.1421449714.git.geoff@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote: > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h > index 99c319c..4f23a48 100644 > --- a/arch/arm64/include/asm/virt.h > +++ b/arch/arm64/include/asm/virt.h > @@ -41,6 +41,19 @@ > > #define HVC_CALL_HYP 3 > > +/* > + * HVC_CALL_FUNC - Execute a function at EL2. > + * > + * @x0: Physical address of the function to be executed. > + * @x1: Passed as the first argument to the function. > + * @x2: Passed as the second argument to the function. > + * @x3: Passed as the third argument to the function. > + * > + * The called function must preserve the contents of register x18. Can you pick a register that's normally callee saved? > + */ > + > +#define HVC_CALL_FUNC 4 > + > #ifndef __ASSEMBLY__ > > /* > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > index e3db3fd..b5d36e7 100644 > --- a/arch/arm64/kernel/hyp-stub.S > +++ b/arch/arm64/kernel/hyp-stub.S > @@ -66,9 +66,20 @@ el1_sync: > mrs x0, vbar_el2 > b 2f > > -1: cmp x18, #HVC_SET_VECTORS > - b.ne 2f > - msr vbar_el2, x0 > +1: cmp x18, #HVC_SET_VECTORS This line doesn't seem to have any change, apart from some whitespace. Or did you want to drop the label? > + b.ne 1f > + msr vbar_el2, x0 > + b 2f > + > +1: cmp x18, #HVC_CALL_FUNC > + b.ne 2f > + mov x18, lr > + mov lr, x0 > + mov x0, x1 > + mov x1, x2 > + mov x2, x3 > + blr lr > + mov lr, x18 > > 2: eret > ENDPROC(el1_sync) What is the calling convention for this HVC? You mentioned x18 above but what about other registers that the called function may corrupt (x18 is a temporary register, so it's not expected to be callee saved).
On Tue, Jan 27, 2015 at 05:39:47PM +0000, Catalin Marinas wrote: > On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote: > > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h > > index 99c319c..4f23a48 100644 > > --- a/arch/arm64/include/asm/virt.h > > +++ b/arch/arm64/include/asm/virt.h > > @@ -41,6 +41,19 @@ > > > > #define HVC_CALL_HYP 3 > > > > +/* > > + * HVC_CALL_FUNC - Execute a function at EL2. > > + * > > + * @x0: Physical address of the function to be executed. > > + * @x1: Passed as the first argument to the function. > > + * @x2: Passed as the second argument to the function. > > + * @x3: Passed as the third argument to the function. > > + * > > + * The called function must preserve the contents of register x18. > > Can you pick a register that's normally callee saved? We're in the hyp-stub, so we don't have a stack in EL2. Therefore we can't stack any of the existing callee-saved register values in order to be able to use them. One way to avoid that would be to have asm block which issues the HVC at EL1 stack/unstack the LR around the HVC. Then we're free to corrupt the LR at EL2 in order to call the provided function. [...] > > +1: cmp x18, #HVC_CALL_FUNC > > + b.ne 2f > > + mov x18, lr > > + mov lr, x0 > > + mov x0, x1 > > + mov x1, x2 > > + mov x2, x3 > > + blr lr > > + mov lr, x18 > > > > 2: eret > > ENDPROC(el1_sync) > > What is the calling convention for this HVC? You mentioned x18 above but > what about other registers that the called function may corrupt (x18 is > a temporary register, so it's not expected to be callee saved). Other than x18, the usual PCS rules apply here. We don't have a stack, so the function we call can't make a nested call to anything else. Mark.
Hi Catalin, On Tue, 2015-01-27 at 17:39 +0000, Catalin Marinas wrote: > On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote: > > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h > > index 99c319c..4f23a48 100644 > > --- a/arch/arm64/include/asm/virt.h > > +++ b/arch/arm64/include/asm/virt.h > > @@ -41,6 +41,19 @@ > > > > #define HVC_CALL_HYP 3 > > > > +/* > > + * HVC_CALL_FUNC - Execute a function at EL2. > > + * > > + * @x0: Physical address of the function to be executed. > > + * @x1: Passed as the first argument to the function. > > + * @x2: Passed as the second argument to the function. > > + * @x3: Passed as the third argument to the function. > > + * > > + * The called function must preserve the contents of register x18. > > Can you pick a register that's normally callee saved? Mark covered this in his reply. > > + */ > > + > > +#define HVC_CALL_FUNC 4 > > + > > #ifndef __ASSEMBLY__ > > > > /* > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > > index e3db3fd..b5d36e7 100644 > > --- a/arch/arm64/kernel/hyp-stub.S > > +++ b/arch/arm64/kernel/hyp-stub.S > > @@ -66,9 +66,20 @@ el1_sync: > > mrs x0, vbar_el2 > > b 2f > > > > -1: cmp x18, #HVC_SET_VECTORS > > - b.ne 2f > > - msr vbar_el2, x0 > > +1: cmp x18, #HVC_SET_VECTORS > > This line doesn't seem to have any change, apart from some whitespace. > Or did you want to drop the label? Some whitespace problems got in there from so many rebases. I went through the series and cleaned them up. > > + b.ne 1f > > + msr vbar_el2, x0 > > + b 2f > > + > > +1: cmp x18, #HVC_CALL_FUNC > > + b.ne 2f > > + mov x18, lr > > + mov lr, x0 > > + mov x0, x1 > > + mov x1, x2 > > + mov x2, x3 > > + blr lr > > + mov lr, x18 > > > > 2: eret > > ENDPROC(el1_sync) > > What is the calling convention for this HVC? You mentioned x18 above but > what about other registers that the called function may corrupt (x18 is > a temporary register, so it's not expected to be callee saved). Again, Mark covered this in his reply.
diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h index 99c319c..4f23a48 100644 --- a/arch/arm64/include/asm/virt.h +++ b/arch/arm64/include/asm/virt.h @@ -41,6 +41,19 @@ #define HVC_CALL_HYP 3 +/* + * HVC_CALL_FUNC - Execute a function at EL2. + * + * @x0: Physical address of the function to be executed. + * @x1: Passed as the first argument to the function. + * @x2: Passed as the second argument to the function. + * @x3: Passed as the third argument to the function. + * + * The called function must preserve the contents of register x18. + */ + +#define HVC_CALL_FUNC 4 + #ifndef __ASSEMBLY__ /* diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S index e3db3fd..b5d36e7 100644 --- a/arch/arm64/kernel/hyp-stub.S +++ b/arch/arm64/kernel/hyp-stub.S @@ -66,9 +66,20 @@ el1_sync: mrs x0, vbar_el2 b 2f -1: cmp x18, #HVC_SET_VECTORS - b.ne 2f - msr vbar_el2, x0 +1: cmp x18, #HVC_SET_VECTORS + b.ne 1f + msr vbar_el2, x0 + b 2f + +1: cmp x18, #HVC_CALL_FUNC + b.ne 2f + mov x18, lr + mov lr, x0 + mov x0, x1 + mov x1, x2 + mov x2, x3 + blr lr + mov lr, x18 2: eret ENDPROC(el1_sync)
Add the new hcall HVC_CALL_FUNC that allows execution of a function at EL2. During CPU reset the CPU must be brought to the exception level it had on entry to the kernel. The HVC_CALL_FUNC hcall will provide the mechanism needed for this exception level switch. Signed-off-by: Geoff Levand <geoff@infradead.org> --- arch/arm64/include/asm/virt.h | 13 +++++++++++++ arch/arm64/kernel/hyp-stub.S | 17 ++++++++++++++--- 2 files changed, 27 insertions(+), 3 deletions(-)