Re: [PATCHv7 14/14] x86/tdx: Add unaccepted memory support

[Borislav Petkov]

On Tue, Jun 14, 2022 at 03:02:31PM +0300, Kirill A. Shutemov wrote:
> +static bool is_tdx_guest(void)
> +{
> +	static bool once;
> +	static bool is_tdx;
> +
> +	if (!IS_ENABLED(CONFIG_INTEL_TDX_GUEST))
> +		return false;
> +
> +	if (!once) {
> +		u32 eax, sig[3];
> +
> +		cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax,
> +			    &sig[0], &sig[2],  &sig[1]);
> +		is_tdx = !memcmp(TDX_IDENT, sig, sizeof(sig));
> +		once = true;
> +	}
> +
> +	return is_tdx;
> +}

early_tdx_detect() already calls this CPUID function. It assigns
function pointers too.

So why can't you assign an accept_memory() function pointer there and
get rid of this sprinkled if (tdx) everywhere?

> diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
> index 918a7606f53c..8518a75e5dd5 100644
> --- a/arch/x86/boot/compressed/tdx.c
> +++ b/arch/x86/boot/compressed/tdx.c
> @@ -3,12 +3,15 @@
>  #include "../cpuflags.h"
>  #include "../string.h"
>  #include "../io.h"
> +#include "align.h"
>  #include "error.h"
> +#include "pgtable_types.h"
>  
>  #include <vdso/limits.h>
>  #include <uapi/asm/vmx.h>
>  
>  #include <asm/shared/tdx.h>
> +#include <asm/page_types.h>
>  
>  /* Called from __tdx_hypercall() for unrecoverable failure */
>  void __tdx_hypercall_failed(void)
> @@ -75,3 +78,78 @@ void early_tdx_detect(void)
>  	pio_ops.f_outb = tdx_outb;
>  	pio_ops.f_outw = tdx_outw;
>  }
> +
> +static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
> +				    enum pg_level level)

That's pretty much a copy of the same function in arch/x86/coco/tdx/tdx.c.

Yeah, you need a tdx-shared.c which you include in both places just like
it is done with sev-shared.c

...

> +void tdx_accept_memory(phys_addr_t start, phys_addr_t end)

That one too.

> +{
> +	/*
> +	 * Notify the VMM about page mapping conversion. More info about ABI
> +	 * can be found in TDX Guest-Host-Communication Interface (GHCI),
> +	 * section "TDG.VP.VMCALL<MapGPA>"
> +	 */
> +	if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
> +		error("Accepting memory failed\n");
> +
> +	/*
> +	 * For shared->private conversion, accept the page using
> +	 * TDX_ACCEPT_PAGE TDX module call.
> +	 */
> +	while (start < end) {
> +		unsigned long len = end - start;
> +		unsigned long accept_size;
> +
> +		/*
> +		 * Try larger accepts first. It gives chance to VMM to keep
> +		 * 1G/2M Secure EPT entries where possible and speeds up
> +		 * process by cutting number of hypercalls (if successful).
> +		 */
> +
> +		accept_size = try_accept_one(start, len, PG_LEVEL_1G);
> +		if (!accept_size)
> +			accept_size = try_accept_one(start, len, PG_LEVEL_2M);
> +		if (!accept_size)
> +			accept_size = try_accept_one(start, len, PG_LEVEL_4K);
> +		if (!accept_size)
> +			error("Accepting memory failed\n");
> +		start += accept_size;

This series of calls to try_accept_one() appear in at least three
places. Please carve them out into a separate function can put it in
tdx-shared.c.

-- 
Regards/Gruss,
    Boris.

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